Software Engineering

UNIT 1 SOFTWARE ENGINEERING and its Model

AND ITS MODELS

Structure Page Nos.
1.0 Introduction 5
1.1 Objectives 6
1.2 Evolution of Software Engineering 6
1.3 Software Development Models 7
1.3.1 Importance of Software Engineering
1.3.2 Various Development Models
1.4 Capability Maturity Models 12
1.4.1 Maturity Levels
1.4.2 Key Process Areas
1.5 Software Process Technology 15
1.6 Summary 20
1.7 Solutions/Answers 20
1.8 Further Readings 21

1.0 INTRODUCTION

The field of software engineering is related to the development of software. Large

software needs systematic development unlike simple programs which can be
developed in isolation and there may not be any systematic approach being followed.

In the last few decades, the computer industry has undergone revolutionary changes in
hardware. That is, processor technology, memory technology, and integration of
devices have changed very rapidly. As the software is required to maintain
compatibility with hardware, the complexity of software also has changed much in the
recent past. In 1970s, the programs were small, simple and executed on a simple
uniprocessor system. The development of software for such systems was much easier.
In the present situation, high speed multiprocessor systems are available and the
software is required to be developed for the whole organisation. Naturally, the
complexity of software has increased many folds. Thus, the need for the application
of engineering techniques in their development is realised. The application of
engineering approach to software development lead to the evolution of the area of
Software Engineering. The IEEE glossary of software engineering terminology
defines the Software Engineering as:

“(a) The application of a systematic, disciplined, quantifiable approach to the

development, operation and maintenance of software, that is, the application of
engineering to software. (b) The study of approaches in (a).”

There is a difference between programming and Software Engineering. Software

Engineering includes activities like cost estimation, time estimation, designing,
coding, documentation, maintenance, quality assurance, testing of software etc.
whereas programming includes only the coding part. Thus, it can be said that
programming activity is only a subset of software development activities. The above
mentioned features are essential features of software. Besides these essential features,
additional features like reliability, future expansion, software reuse etc. are also
considered. Reliability is of utmost importance in real time systems like flight control,
medical applications etc.

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An Overview of
Software Engineering 1.1 OBJECTIVES
After going through this unit, you should be able to:

• define software engineering;

• understand the evolution of software engineering;
• understand the characteristics of software;
• learn about phases of software development life cycle, and
• understand software development models.

1.2 EVOLUTION OF SOFTWARE ENGINEERING

Any application on computer runs through software. As computer technologies have
changed tremendously in the last five decades, accordingly, the software development
has undergone significant changes in the last few decades of 20th century. In the early
years, the software size used to be small and those were developed either by a single
programmer or by a small programming team. The program development was
dependent on the programmer’s skills and no strategic software practices were
present. In the early 1980s, the size of software and the application domain of
software increased. Consequently, its complexity has also increased. Bigger teams
were engaged in the development of Software. The software development became
more bit organised and software development management practices came into
existence.

In this period, higher order programming languages like PASCAL and COBOL came
into existence. The use of these made programming much easier. In this decade, some
structural design practices like top down approach were introduced. The concept of
quality assurance was also introduced. However, the business aspects like cost
estimation, time estimation etc. of software were in their elementary stages.

In the late 1980s and 1990s, software development underwent revolutionary changes.
Instead of a programming team in an organisation, full-fledged software companies
evolved (called software houses). A software houses primary business is to produce
software. As software house may offer a range of services, including hiring out of
suitably qualified personnel to work within client’s team, consultancy and a complete
system design and development service. The output of these companies was
‘Software’. Thus, they viewed the software as a product and its functionality as a
process. The concept of software engineering was introduced and Software became
more strategic, disciplined and commercial. As the developer of Software and user of
Software became separate organisation, business concepts like software costing,
Software quality, laying of well-defined requirements, Software reliability, etc., came
into existence. In this phase an entirely new computing environments based on a
knowledge-based systems get created. Moreover, a powerful new concept of object-
oriented programming was also introduced.

The production of software became much commercial. The software development

tools were devised. The concept of Computer Aided Software Engineering (CASE)
tools came into existence. The software development became faster with the help of
CASE tools.

The latest trend in software engineering includes the concepts of software reliability,
reusability, scalability etc. More and more importance is now given to the quality of
the software product. Just as automobile companies try to develop good quality
automobiles, software companies try to develop good quality Software. The software
creates the most valuable product of the present era, i.e., information.

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The following Table summarises the evolution of software: Software Engineering
and its Model
1960s Infancy Machine Code
1970s Project Years Higher Order Languages
1980s Project Years Project Development
1990s Process and Production Era Software Reuse

The problems arising in the development of software is termed as crisis. It includes

the problems arising in the process of development of software rather than software
functioning. Besides development, the problems may be present in the maintenance
and handling of large volumes of software. Some of the common misunderstandings
regarding software development are given below.

1. Correcting errors is easy. Though the changes in the software are possible, but,
making changes in large software is extremely difficult task.

2. By proper development of software, it can function perfectly at first time.

Though, theoretically, it seems correct, but practically software undergoes many
development/coding/testing passes before becoming perfect for working.

3. Loose objective definition can be used at starting point. Once a software is

developed using loose objective, changing it for specific objectives may require
complete change.

4. More manpower can be added to speed up the development. Software is

developed by well coordinated teams. Any person joining it at a later stage may
require extra efforts to understand the code.

Software Standards

Various terms related to software engineering are regularly standardised by

organisations like IEEE (Institute of Electrical and Electronics Engineers), ANSI
(American National Standards Institute), OMG (Object Management Group), CORBA
(Common Object Request Broker Architecture).

IEEE regularly publishes software development standards.

OMG is international trade organisation (http://www.omg.org) and is one of the

largest consortiums in the software industry. CORBA defines the standard capabilities
that allow objects to interact with each other.

1.3 SOFTWARE DEVELOPMENT MODELS

Software Engineering deals with the development of software. Hence, understanding
the basic characteristics of software is essential. Software is different from other
engineering products in the following ways:

1. Engineering products once developed cannot be changed. To modifications the

product, redesigning and remanufacturing is required. In the case of software,
ultimately changes are to be done in code for any changes to take effect.

2. The Other Engineering products are visible but the software as such is not
visible. That’s why, it is said that software is developed, but not manufactured.
Though, like other products, it is first designed, then produced, it cannot be
manufactured automatically on an assembly line like other engineering
products. Nowadays, CASE (Computer Aided Software Engineering) tools are
available for software development. Still it depends on the programmer’s skill
and creativity. The creative skills of the programmer is difficult to quantify and
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An Overview of standardise. Hence, the same software developed by different programmers
Software Engineering
may take varying amount of time, resources and may have variable cost.

3. Software does not fail in the traditional sense. The engineering products has
wear and tear in the operation. Software can be run any number of times
without wear and tear. The software is considered as failed if:

a) It does not operate correctly.

b) Does not provide the required number of features.

4. Engineering products can be perfectly designed, but in the case of software,

however good the design, it can never be 100% error free. Even the best quality
software is not completely error free. A software is called good quality software
if it performs the required operation, even if it has a few errors.

5. The testing of normal engineering products and software engineering products

are on different parameters. In the former, it can be full load testing, etc.,
whereas in the case of software, testing means identification of test cases in
which software may fail. Thus, testing of software means running of software
for different inputs. By testing, the presence of errors is identified.

6. Unlike most of the other engineering products, software can be reused. Once a
piece of code is written for some application, it can be reused.

7. The management of software development projects is a highly demanding task,

since it involves the assessment of the developers creative skills. The
estimation regarding the time and cost of software needs standardisation of
developers creativity, which can be a variable quantity. It means that software
projects cannot be managed like engineering products. The correction of a bug
in the case of software may take hours But, it may not be the case with normal
engineering products.

8. The Software is not vulnerable to external factors like environmental effects.

But the same external factors may harm hardware. The hardware component
may be replaced with spare parts in the case of failure, whereas the failure of a
software component may indicate the errors in design.

Thus, the characteristics of software are quite different from other engineering
products. Hence, the software industry is quite different from other industries.

1.3.1 Importance of Software Engineering

As the application domains of software are becoming complicated and design of big
software without a systematic approach is virtually impossible, the field of software
engineering is increasingly gaining importance. It is now developing like an industry.
Thus, the industry has to answer following or similar queries of clients:

1) What is the best approach to design of software?

2) Why the cost of software is too high?
3) Why can’t we find all errors?
4) Why is there always some gap between claimed performance and actual
performance?

To answer all such queries, software development has adopted a systematic approach.

Software development should not remain an art. Scientific basis for cost, duration,
risks, defects etc. are required. For quality assurance, product qualities and process
qualities and must be made measurable as far as possible by developing metrics for
them.
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1.3.2 Various Development Models Software Engineering
and its Model
The following are some of the models adopted to develop software:

(i) Build and Fix Model

It is a simple two phase model. In one phase, code is developed and in another, code
is fixed.

Figure 1.1 depicts the Build and Fix model.

Fix the code Deliver the

Develop Code until the client product
is satisfied

Figure 1.1 : Build and fix model

(ii) Waterfall Model

It is the simplest, oldest and most widely used process model. In this model, each
phase of the life cycle is completed before the start of a new phase. It is actually the
first engineering approach of software development.

Figure 1.2 depicts Water Fall Model.

Requirements analysis

Design

Coding

Testing

Maintenance

Figure 1.2 : Water fall model

The functions of various phases are discussed in software process technology.

The waterfall model provides a systematic and sequential approach to software

development and is better than the build and fix approach. But, in this model,
complete requirements should be available at the time of commencement of the
project, but in actual practice, the requirements keep on originating during different
phases. The water fall model can accommodate the new requirements only in
maintenance phase. Moreover, it does not incorporate any kind of risk assessment. In
waterfall model, a working model of software is not available. Thus, there is no
methods to judge the problems of software in between different phases.

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An Overview of A slight modification of the waterfall model is a model with feedback. Once software
Software Engineering
is developed and is operational, then the feedback to various phases may be given.
Figure 1.3 depicts the Water Fall Model with feedback.

Requirements Analysis

Design

Coding

Testing

Maintenance

Figure 1.3 : Water fall model with feedback

(iii) Iterative Enhancement Model

This model was developed to remove the shortcomings of waterfall model. In this
model, the phases of software development remain the same, but the construction and
delivery is done in the iterative mode. In the first iteration, a less capable product is
developed and delivered for use. This product satisfies only a subset of the
requirements. In the next iteration, a product with incremental features is developed.
Every iteration consists of all phases of the waterfall model. The complete product is
divided into releases and the developer delivers the product release by release.

Figure 1.4 depicts the Iterative Enhancement Model.

Iteration-1 Iteration-2

Water fall Model Water fall Model

Figure 1.4 : Iterative enhancement model

This model is useful when less manpower is available for software development and
the release deadlines are tight. It is best suited for in-house product development,
where it is ensured that the user has something to start with. The main disadvantage of
this model is that iteration may never end, and the user may have to endlessly wait for
the final product. The cost estimation is also tedious because it is difficult to relate the
software development cost with the number of requirements.

(iv) Prototyping Model

In this model, a working model of actual software is developed initially. The

prototype is just like a sample software having lesser functional capabilities and low
reliability and it does not undergo through the rigorous testing phase. Developing a
working prototype in the first phase overcomes the disadvantage of the waterfall
model where the reporting about serious errors is possible only after completion of
software development.
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The working prototype is given to the customer for operation. The customer, after its Software Engineering
and its Model
use, gives the feedback. Analysing the feedback given by the customer, the developer
refines, adds the requirements and prepares the final specification document. Once the
prototype becomes operational, the actual product is developed using the normal
waterfall model. Figure 1.5 depicts the prototyping model.
The prototype model has the following features:
(i) It helps in determining user requirements more deeply.
(ii) At the time of actual product development, the customer feedback is available.
(iii) It does consider any types of risks at the initial level.
Feedback

Quick Plan Quick Design Develop prototype Deliver to customer

Start
Figure 1.5: Prototyping model

(v) Spiral Model

This model can be considered as the model, which combines the strengths of various
other models. Conventional software development processes do not take uncertainties
into account. Important software projects have failed because of unforeseen risks.
The other models view the software process as a linear activity whereas this model
considers it as a spiral process. This is made by representing the iterative
development cycle as an expanding spiral.
The following are the primary activities in this model:
• Finalising Objective: The objectives are set for the particular phase of the
project.
• Risk Analysis: The risks are identified to the extent possible. They are analysed
and necessary steps are taken.
• Development: Based on the risks that are identified, an SDLC model is selected
and is followed.
• Planning: At this point, the work done till this time is reviewed. Based on the
review, a decision regarding whether to go through the loop of spiral again or not
will be decided. If there is need to go, then planning is done accordingly.
In the spiral model, these phases are followed iteratively. Figure 1.6 depicts the
Boehm’s Spiral Model (IEEE, 1988).

Figure 1.6: Spiral model

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An Overview of In this model Software development starts with lesser requirements specification,
Software Engineering
lesser risk analysis, etc. The radical dimension this model represents cumulative cost.
The angular dimension represents progress made in completing the cycle.

The inner cycles of the spiral model represent early phases of requirements analysis
and after prototyping of software, the requirements are refined.

In the spiral model, after each phase a review is performed regarding all products
developed upto that point and plans are devised for the next cycle. This model is a
realistic approach to the development of large scale software. It suggests a systematic
approach according to classical life cycle, but incorporates it into iterative framework.
It gives a direct consideration to technical risks. Thus, for high risk projects, this
model is very useful. The risk analysis and validation steps eliminate errors in early
phases of development.

(vi) RAD Approach

As the name suggests, this model gives a quick approach for software development
and is based on a linear sequential flow of various development processes. The
software is constructed on a component basis. Thus multiple teams are given the task
of different component development. It increases the overall speed of software
development. It gives a fully functional system within very short time. This approach
emphasises the development of reusable program components. It follows a modular
approach for development. The problem with this model is that it may not work when
technical risks are high.
& Check Your Progress 1
1) Indicate various problems related with software development.
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2) Give a comparative analysis of various types of software process models.
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3) What are various phases of software development life cycle?
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1.4 CAPABILITY MATURITY MODELS

The process models are based on various software development phases whereas the
capability models have an entirely different basis of development. They are based
upon the capabilities of software. It was developed by Software Engineering
Institute (SEI). In this model, significant emphasis is given to the techniques to
improve the “software quality” and “process maturity”. In this model a strategy for
improving Software process is devised. It is not concerned which life cycle mode is
followed for development. SEI has laid guidelines regarding the capabilities an

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organisation should have to reach different levels of process maturity. This approach Software Engineering
and its Model
evaluates the global effectiveness of a software company.
1.4.1 Maturity Levels
It defines five maturity levels as described below. Different organisations are certified
for different levels based on the processes they follow.
Level 1 (Initial): At this maturity level, software is developed an ad hoc basis and no
strategic approach is used for its development. The success of developed software
entirely depend upon the skills of the team members. As no sound engineering
approach is followed, the time and cost of the project are not critical issues. In
Maturity Level 1 organisations, the software process is unpredictable, because if the
developing team changes, the process will change. The testing of software is also
very simple and accurate predictions regarding software quality are not possible.
SEI’s assessment indicates that the vast majority of software organisations are Level 1
organisations.
Level 2 (Repeatable): The organisation satisfies all the requirements of level-1. At
this level, basic project management policies and related procedures are established.
The institutions achieving this maturity level learn with experience of earlier projects
and reutilise the successful practices in on-going projects. The effective process can
be characterised as practised, documented, implemented and trained. In this maturity
level, the manager provides quick solutions to the problem encountered in software
development and corrective action is immediately taken. Hence, the process of
development is much disciplined in this maturity level. Thus, without measurement,
sufficiently realistic estimates regarding cost, schedules and functionality are
performed. The organisations of this maturity level have installed basic management
controls.
Level 3 (Defined): The organisation satisfies all the requirements of level-2. At this
maturity level, the software development processes are well defined, managed and
documented. Training is imparted to staff to gain the required knowledge. The
standard practices are simply tailored to create new projects.

Level 4 (Managed): The organisation satisfies all the requirements of level-3. At this
level quantitative standards are set for software products and processes. The project
analysis is done at integrated organisational level and collective database is created.
The performance is measured at integrated organisation level. The Software
development is performed with well defined instruments. The organisation’s
capability at Level 4 is “predictable” because projects control their products and
processes to ensure their performance within quantitatively specified limits. The
quality of software is high.
Level 5 (Optimising): The organisation satisfies all the requirements of level-4. This
is last level. The organisation at this maturity level is considered almost perfect. At
this level, the entire organisation continuously works for process improvement with
the help of quantitative feedback obtained from lower level. The organisation analyses
its weakness and takes required corrective steps proactively to prevent the errors.
Based on the cost benefit analysis of new technologies, the organisation changes their
Software development processes.

1.4.2 Key Process Areas

The SEI has associated key process areas (KPAs) with each maturity level. The KPA
is an indicative measurement of goodness of software engineering functions like
project planning, requirements management, etc. The KPA consists of the following
parameters:
Goals: Objectives to be achieved.
Commitments: The requirements that the organisation should meet to ensure the
claimed quality of product.
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An Overview of Abilities : The capabilities an organisation has.
Software Engineering
Activities : The specific tasks required to achieve KPA function.

Methods for varying implementation: It explains how the KPAs can be verified.

18 KPAs are defined by SEI and associated with different maturity levels. These are
described below:

Level 1 KPAs : There is no key process area at Level 1.

Level 2 KPAs:

1) Software Project Planning: Gives concrete plans for software management.

2) Software Project Tracing & Oversight: Establish adequate visibility into

actual process to enable the organisation to take immediate corrective steps
if Software performance deviates from plans.

3) Requirements Management: The requirements are well specified to develop a

contract between developer and customer.

4) Software Subcontract Management: Select qualified software subcontractors

and manage them effectively.

5) Software Quality Assurance (SQA): To Assure the quality of developed

product.

6) Software Configuration Management (SCM): Establish & maintain integrity

through out the lifecycle of project.

Level 3 KPAs:

1) Organisation Process Focus (OPF): The organisations responsibility is fixed

for software process activities that improve the ultimate software process
capability.

2) Training Program (TP): It imparts training to develop the skills and

knowledge of organisation staff.

3) Organisation Process Definition (OPD): It develops a workable set of

software process to enhance cumulative long term benefit of organisation by
improving process performance.

4) Integrated Software Management (ISM): The software management and

software engineering activities are defined and a tailor made standard and
software process suiting to organisations requirements is developed.

5) Software Product Engineering (SPE): Well defined software engineering

activities are integrated to produce correct, consistent software products
effectively and efficiently.

6) Inter group co-ordination (IC): To satisfy the customer’s needs effectively

and efficiently, Software engineering groups are created. These groups
participate actively with other groups.

7) Peer reviews (PR): They remove defects from software engineering work
products.

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Level 4 KPAs: Software Engineering
and its Model
1) Quantitative Process Management (QP): It defines quantitative standards for
software process.

2) Software Quality Management (SQM): It develops quantitative

understanding of the quality of Software products and achieves specific quality
goals.

Level 5 KPAs:

1) Defect Prevention (DP): It discovers the causes of defects and devises the
techniques which prevent them from recurring.

2) Technology Change Management (TCM): It continuously upgrades itself

according to new tools, methods and processes.

3) Process Change Management (PCM): It continually improves the software

processes used in organisation to improve software quality, increase
productivity and decrease cycle time for product development.

& Check Your Progress 2

1) What are different levels of capability maturity model?

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2) What is the level of CMM with which no KPA is associated?
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1.5 SOFTWARE PROCESS TECHNOLOGY

The software industry considers software development as a process. According to
Booch and Rumbaugh, “A process defines who is doing what, when and how to reach
a certain goal?” Software engineering is a field which combines process, methods and
tools for the development of software. The concept of process is the main step in the
software engineering approach. Thus, a software process is a set of activities. When
those activities are performed in specific sequence in accordance with ordering
constraints, the desired results are produced. A software development project requires
two types of activities viz., development and project management activities. These
activities together comprise of a software process. As various activities are being
performed in software process, these activities are categorized into groups called
phases. Each phase performs well defined activities.

The various steps (called phases) which are adopted in the development of this
process are collectively termed as Software Development Life Cycle (SDLC). The
various phases of SDLC are discussed below. Normally, these phases are performed
lineally or circularly, but it can be changed according to project as well. The software
is also considered as a product and its development as a process. Thus, these phases

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An Overview of can be termed as Software Process Technology. In general, different phases of SDLC
Software Engineering
are defined as following:
• Requirements Analysis
• Design
• Coding
• Software Testing
• Maintenance.

Let us discuss these steps in detail.

Requirements Analysis

Requirements describe the “What” of a system. The objectives which are to be

achieved in Software process development are the requirements. In the requirements
analysis phase, the requirements are properly defined and noted down. The output of
this phase is SRS (Software Requirements Specification) document written in natural
language. According to IEEE, requirements analysis may be defined as (1) the process
of studying user’s needs to arrive at a definition of system hardware and software
requirements (2) the process of studying and refining system hardware or software
requirements.

Design

In this phase, a logical system is built which fulfils the given requirements. Design
phase of software development deals with transforming the customer’s requirements
into a logically working system. Normally, design is performed in the following two
steps:

i) Primary Design Phase: In this phase, the system is designed at block level.
The blocks are created on the basis of analysis done in the problem
identification phase. Different blocks are created for different functions
emphasis is put on minimising the information flow between blocks. Thus, all
activities which require more interaction are kept in one block.

ii) Secondary Design Phase: In the secondary design phase the detailed design of
every block is performed.

The input to the design phase is the Software Requirements Specification (SRS)
document and the output is the Software Design Document (SDD). The general tasks
involved in the design process are the following:

i) Design various blocks for overall system processes.

ii) Design smaller, compact, and workable modules in each block.
iii) Design various database structures.
iv) Specify details of programs to achieve desired functionality.
v) Design the form of inputs, and outputs of the system.
vi) Perform documentation of the design.
vii) System reviews.

The Software design is the core of the software engineering process and the first of
three important technical activities, viz., design, coding, and testing that are required
to build software. The design should be done keeping the following points in mind.

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i) It should completely and correctly describe the system. Software Engineering
and its Model
ii) It should precisely describe the system. It should be understandable to the
software developer.

iii) It should be done at the right level.

iv) It should be maintainable.

The following points should be kept in mind while performing the design:

i) Practicality: This ensures that the system is stable and can be operated by a
person of average intelligence.

ii) Efficiency: This involves accuracy, timeliness and comprehensiveness of

system output.

iii) Flexibility: The system could be modifiable depending upon changing needs of
the user. Such amendments should be possible with minimum changes.

iv) Security: This is an important aspect of design and should cover areas of
hardware reliability, fall back procedures, security of data and provision for
detection of fraud.

Coding

The input to the coding phase is the SDD document. In this phase, the design
document is coded according to the module specification. This phase transforms the
SDD document into a high level language code. At present major software companies
adhere to some well specified and standard style of coding called coding standards.
Good coding standards improve the understanding of code. Once a module is
developed, a check is carried out to ensure that coding standards are followed. Coding
standards generally give the guidelines about the following:

i) Name of the module

ii) Internal and External documentation of source code
iii) Modification history
iv) Uniform appearance of codes.

Testing

Testing is the process of running the software on manually created inputs with the
intention to find errors. In the process of testing, an attempt is made to detect errors, to
correct the errors in order to develop error free software. The testing is performed
keeping the user’s requirements in mind and before the software is actually launched
on a real system, it is tested. Testing is the process of executing a program with the
intention of finding errors.

Normally, while developing the code, the software developer also carries out some
testing. This is known as debugging. This unearths the defects that must be removed
from the program. Testing and debugging are different processes. Testing is meant for
finding the existence of defects while debugging stands for locating the place of errors
and correcting the errors during the process of testing. The following are some
guidelines for testing:

i) Test the modules thoroughly, cover all the access paths, generate enough data to
cover all the access paths arising from conditions.
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An Overview of ii) Test the modules by deliberately passing wrong data.
Software Engineering
iii) Specifically create data for conditional statements. Enter data in test file which
would satisfy the condition and again test the script.

iv) Test for locking by invoking multiple concurrent processes.

The following objectives are to be kept in mind while performing testing:

i) It should be done with the intention of finding the errors.

ii) Good test cases should be designed which have a probability of finding, as yet
undiscovered error.

iii) A success test is one that uncovers yet undiscovered error(s).

The following are some of the principles of testing:

i) All tests should be performed according to user requirements.

ii) Planning of tests should be done long before testing.

iii) Starting with a small test, it should proceed towards large tests.

The following are different levels of testing:

Large systems are built out of subsystems, subsystems are made up of modules,
modules of procedures and functions. Thus in large systems, the testing is performed
at various levels, like unit level testing, module level testing, subsystem level, and
system level testing.

Thus, testing is performed at the following levels. In all levels, the testing are
performed to check interface integrity, information content, performance.

The following are some of the strategies of testing: This involves design of test cases.
Test case is set of designed data for which the system is tested. Two testing strategies
are present.

i) Code Testing: The code testing strategy examines the logic of the system. In
this, the analyst develops test cases for every instruction in the code. All the
paths in the program are tested. This test does not guarantee against software
failures. Also, it does not indicate whether the code is according to
requirements or not.

ii) Specification Testing: In this, testing with specific cases is performed. The
test cases are developed for each condition or combination of conditions and
submitted for processing.

The objective of testing is to design test cases that systematically uncover different
classes of errors and do so with the minimum amount of time and effort. Testing
cannot show the absence of errors. It can only find the presence of errors. The test
case design is as challenging as software development. Still, however effective the
design is, it cannot remove 100% errors. Even, the best quality software are not 100 %
error free. The reliability of software is closely dependent on testing.

Some testing techniques are the black box and the white box methods.

White box testing: This method, also known as glass box testing, is performed early
in the testing process. Using this, the software engineer can derive a tests that

18
guarantees that all independent paths within the module have been exercised at least Software Engineering
and its Model
once. It has the following features:

i) Exercise all logical decisions on their true and false sides.

ii) Execute all loops at their boundaries and within their operational bounds.

iii) Exercise internal data structures to assure their validity.

Black box testing: This is applied during the later stage of testing. It enables the
software developer to derive a set of input conditions that will fully exercise the
functional requirements of a program. It enables him to find errors like incorrect or
missing functions, interface errors, data structures or external data base access errors
and performance errors etc.

Maintenance

Maintenance in the normal sense means correcting the problems caused by wear and
tear, but software maintenance is different. Software is either wrong in the beginning
or later as some additional requirements have been added. Software maintenance is
done because of the following factors.

i) To rectify the errors which are encountered during the operation of software.

ii) To change the program function to interface with new hardware or software.

iii) To change the program according to increased requirements.

There are three categories of maintenance:

i) Corrective Maintenance
ii) Adaptive Maintenance
iii) Perfective Maintenance

Software maintenance is a very broad activity that includes error correction,

enhancement of capabilities, deletion of obsolete capabilities, and optimisation
[STEP 78]. Hence, once the software becomes operational, whatever changes are done
are termed as maintenance. As the software requirement change continuously,
maintenance becomes a continuous process. In practice, the cost of software
maintenance is far more than the cost of software development. It accounts for 50% to
80% of the total system development costs. The Software maintenance has the
following problems:

i) It is very cumbersome to analyse and understand the code written by somebody.

ii) No standards for maintenance have been developed and the area is relatively
unexplored area.

iii) Few tools and techniques are available for maintenance.

iv) It is viewed as a necessary evil and delegated to junior programmers.

The various phases of the software development life cycle are tightly coupled, and the
output of one phase governs the activity of the subsequent phase. Thus, all the phases
need to be carefully planned and managed and their interaction requires close
monitoring. The project management becomes critical in larger systems.

19
An Overview of
Software Engineering 1.6 SUMMARY
Software engineering covers the entire range of activities used to develop software.
The activities include requirements analysis, program development using some
recognised approach like structured programming, testing techniques, quality
assurance, management and implementation and maintenance. Further, software
engineering expects to address problems which are encountered during software
development.

1.7 SOLUTIONS/ANSWERS

Check Your Progress 1

1) The following are major problems related with software development:

• There may be multiple models suitable to do project. How to decide the

best one?

• The understanding of user requirements may be incomplete.

• The problem of less documentation or minimal structured techniques may

be there.

• The last minute changes in implementation issues give rise to problems

elated with hardware.

2) Out of all SDLC models, the most popular one is waterfall model. But, it insists
on having a complete set of requirements before commencement of design. It is
often difficult for the customer to state all requirements easily. The iterative
enhancement model, though better than waterfall model, in customised software
development where the client has to provide and approve the specification, it
may lead to time delays for software development. Prototype model provides
better understanding of customer’s needs and is useful for large systems, but, in
this, the use of inefficient inaccurate or dummy functions may produce
undesired results. The spiral model accommodates good features of other
models. In this, risk analysis and validation steps eliminate errors in early
phases of development. But, in this model, there is a lack of explicit process
guidance in determining objectives.

3) Various phases of software development life cycle are:

• Requirement analysis
• Design
• Coding
• Testing
• Maintenance

Check Your Progress 2

1) Initial, Repeatable, Defined, Managed, Optimizable

2) Level-1

20
 Software Engineering
1.8 FURTHER READINGS and its Model

1) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson

Education.

2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman;

McGraw-Hill International Edition.

Reference websites

http://www.rspa.com
http://www.ieee.org
http://standards.ieee.org

21
 An Overview of
Software Engineering UNIT 2 PRINCIPLES OF SOFTWARE
REQUIREMENTS ANALYSIS
Structure Page Nos.

2.0 Introduction 22
2.1 Objectives 23
2.2 Engineering the Product 23
2.2.1 Requirements Engineering
2.2.2 Types of Requirements
2.2.3 Software Requirements Specification (SRS)
2.2.4 Problems in SRS
2.2.5 Requirements Gathering Tools
2.3 Modeling the System Architecture 26
2.3.1 Elementary Modeling Techniques
2.3.2 Data Flow Diagrams
2.3.3 Rules for Making DFD
2.3.4 Data Dictionary
2.3.5 E-R Diagram
2.3.6 Structured Requirements Definition
2.4 Software Prototyping and Specification 34
2.4.1 Types of Prototype
2.4.2 Problems of Prototyping
2.4.3 Advantages of Prototyping
2.5 Software Metrics 35
2.6 Summary 36
2.7 Solutions/Answers 37
2.8 Further Readings 38

2.0 INTRODUCTION
In the design of software, the first step is to decide about the objectives of software.
This is the most difficult aspect of software design. These objectives, which the
software is supposed to fulfill are called requirements.

The IEEE [IEEE Std 610.12] definition of requirement is:

1. A condition or capability needed by a user to solve a problem or achieve an
objective.
2. A condition or capability that must be met or possessed by a system component,
to satisfy a contract formally imposed document.
3. A documented representation of a condition or capability as in (1) or (2).

Thus, requirements specify “what the system is supposed to do?” These requirements
are taken from the user. Defining the requirements is most elementary & most
difficult part of system design, because, at this level, sometimes, the user himself is
not clear about it. Many software projects have failed due to certain requirements
specification issues. Thus, overall quality of software product is dependent on this
aspect. Identifying, defining, and analysing the requirements is known as requirements
analysis. Requirements analysis includes the following activities:
1. Identification of end user’s need.
2. Preparation of a corresponding document called SRS (Software Requirements
Specification).

22
3. Analysis and validation of the requirements document to ensure consistency, Principles of Software
Requirements Analysis
completeness and feasibility.

4. Identification of further requirements during the analysis of mentioned

requirements.

2.1 OBJECTIVES
After going through this unit, you should be able to:

• understand the significance of requirements analysis;

• develop SRS, and
• know various tools and techniques used for requirements analysis.

2.2 ENGINEERING THE PRODUCT

Due to the complexity involved in software development, the engineering approach
is being used in software design. Use of engineering approach in the area of
requirements analysis evolved the field of Requirements Engineering.

2.2.1 Requirements Engineering

Requirements Engineering is the systematic use of proven principles, techniques and

language tools for the cost effective analysis, documentation, on-going evaluation of
user’s needs and the specification of external behaviour of a system to satisfy those
user needs. It can be defined as a discipline, which addresses requirements of objects
all along a system development process.

The output of requirements of engineering process is Requirements Definition

Description (RDD). Requirements Engineering may be defined in the context of
Software Engineering. It divides the Requirements Engineering into two categories.
First is the requirements definition and the second is requirements management.

Requirements definition consists of the following processes:

1. Requirements gathering.

2. Requirements analysis and modeling.

3. Creation of RDD and SRS.

4. Review and validation of SRS as well as obtaining confirmation from user.
Requirements management consists of the following processes:

1. Identifying controls and tracking requirements.

2. Checking complete implementation of RDD.
3. Manage changes in requirements which are identified later.
2.2.2 Types of Requirements
There are various categories of the requirements.
On the basis of their priority, the requirements are classified into the following
three types:
23
 An Overview of 1. Those that should be absolutely met.
Software Engineering 2. Those that are highly desirable but not necessary.
3. Those that are possible but could be eliminated.

On the basis of their functionality, the requirements are classified into the following
two types:

i) Functional requirements: They define the factors like, I/O formats, storage
structure, computational capabilities, timing and synchronization.

ii) Non-functional requirements: They define the properties or qualities of a

product including usability, efficiency, performance, space, reliability,
portability etc.

2.2.3 Software Requirements Specification (SRS)

This document is generated as output of requirement analysis. The requirement

analysis involves obtaining a clear and thorough understanding of the product to be
developed. Thus, SRS should be consistent, correct, unambiguous & complete,
document. The developer of the system can prepare SRS after detailed communication
with the customer. An SRS clearly defines the following:

• External Interfaces of the system: They identify the information which is to flow
‘from and to’ to the system.
• Functional and non-functional requirements of the system. They stand for the
finding of run time requirements.
• Design constraints:

The SRS outline is given below:

1. Introduction
1.1 Purpose
1.2 Scope
1.3 Definitions, acronyms, and abbreviations
1.4 References
1.5 Overview
2. Overall description
2.1 Product perspective
2.2 Product functions
2.3 User characteristics
2.4 Constraints
2.5 Assumptions and dependencies
3. Specific requirements
3.1 External Interfaces
3.2 Functional requirements
3.3 Performance requirements
3.4 Logical Database requirements
3.5 Design Constraints
3.6 Software system attributes
3.7 Organising the specific requirements
3.8 Additional Comments
4. Supporting information
4.1 Table of contents and index
4.2 Appendixes
24
2.2.4 Problems in SRS Principles of Software
Requirements Analysis
There are various features that make requirements analysis difficult. These are
discussed below:
1. Complete requirements are difficult to uncover. In recent trends in engineering,
the processes are automated and it is practically impossible to understand the
complete set of requirements during the commencement of the project itself.
2. Requirements are continuously generated. Defining the complete set of
requirements in the starting is difficult. When the system is put under run, the new
requirements are obtained and need to be added to the system. But, the project
schedules are seldom adjusted to reflect these modifications. Otherwise, the
development of software will never commence.
3. The general trends among software developer shows that they have over
dependence on CASE tools. Though these tools are good helping agents, over
reliance on these Requirements Engineering Tools may create false requirements.
Thus, the requirements corresponding to real system should be understood and
only a realistic dependence on tools should be made.

4. The software projects are generally given tight project schedules. Pressure is
created from customer side to hurriedly complete the project. This normally cuts
down the time of requirements analysis phase, which frequently lead to
disaster(s).
5. Requirements Engineering is communication intensive. Users and developers
have different vocabularies, professional backgrounds and psychology. User
writes specifications in natural language and developer usually demands precise
and well-specified requirement.

6. In present time, the software development is market driven having high

commercial aspect. The software developed should be a general purpose one to
satisfy anonymous customer, and then, it is customised to suit a particular
application.
7. The resources may not be enough to build software that fulfils all the customer’s
requirements. It is left to the customer to prioritise the requirements and develop
software fulfilling important requirements.

2.2.5 Requirements Gathering Tools

The requirements gathering is an art. The person who gathers requirements should
have knowledge of what and when to gather information and by what resources. The
requirements are gathered regarding organisation, which include information
regarding its policies, objectives, and organisation structure, regarding user staff. It
includes the information regarding job function and their personal details, regarding
the functions of the organisation including information about work flow, work
schedules and working procedure.

The following four tools are primarily used for information gathering:

1. Record review: A review of recorded documents of the organisation is

performed. Procedures, manuals, forms and books are reviewed to see format and
functions of present system. The search time in this technique is more.

2. On site observation: In case of real life systems, the actual site visit is performed
to get a close look of system. It helps the analyst to detect the problems of existing
system.

25
 An Overview of 3. Interview: A personal interaction with staff is performed to identify their
Software Engineering requirements. It requires experience of arranging the interview, setting the stage,
avoiding arguments and evaluating the outcome.

4. Questionnaire: It is an effective tool which requires less effort and produces a

written document about requirements. It examines a large number of respondents
simultaneously and gets customized answers. It gives person sufficient time to
answer the queries and give correct answers.
) Check Your Progress 1
1) Why is it justified to use engineering approach in requirements analysis?
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………

2.3 MODELING THE SYSTEM ARCHITECTURE

Before the actual system design commences, the system architecture is modeled. In
this section, we discuss various modeling techniques.

2.3.1 Elementary Modeling Techniques

A model showing bare minimum requirements is called Essential Model. It has two
components.

1. Environmental model: It indicates environment in which system exists. Any big

or small system is a sub-system of a larger system. For example, if software is
developed for a college, then college will be part of University. If it is developed
for University, the University will be part of national educational system. Thus,
when the model of the system is made these external interfaces are defined. These
interfaces reflect system’s relationship with external universe (called
environment). The environment of a college system is shown in Figure 2.1.

Courses offered
to students

Department

College
Interfaces to
external systems
University

National Educational System

Figure 2.1 : Environmental model of educational system

In environmental model, the interfaces should clearly indicate the inflow and outflow
of information from the system.
26
The tools of environment model are: Principles of Software
Requirements Analysis
(i) Statement of purpose: It indicates the basic objectives of system.
(ii) Event list: It describes the different events of system and indicates functionality
of the system.
(iii) Context diagram: It indicates the environment of various sub-systems.

2. Behavioural Model: It describes operational behaviour of the system. In this

model, various operations of the system are represented in pictorial form. The
tools used to make this model are: Data Flow Diagrams (DFD), E-R diagrams,
Data Dictionary & Process Specification. These are discussed in later sections.
Hence, behavioural model defines:
Data of proposed system.
(i) The internal functioning of proposed system,
(ii) Inter-relationship between various data.
In traditional approach of modeling, the analyst collects great deal of relatively
unstructured data through data gathering tools and organize the data through system
flow charts which support future development of system and simplify communication
with the user. But, flow chart technique develops physical rather than logical system.

In structured approach of modeling the standard techniques of DFD, E-R diagram etc.
are used to develop system specification in a formal format. It develops a system
logical model.
2.3.2 Data Flow Diagrams (DFD)
It is a graphical representation of flow of data through a system. It pictures a system as
a network of functional processes. The basis of DFD is a data flow graph, which
pictorially represents transformation on data as shown in Figure 2.2.

Input data Level 1 Input data

External Processing External
Entity Entity

Intermediate data

External Input data Output data External

Level 2
Entity Processing Entity

Intermediate data

Level 3
Processing
Data store

Output data

External
Entity

Figure 2.2: Data flow diagram 27

 An Overview of In this diagram, the external entities provide input data for the processing. During the
Software Engineering processing, some intermediate data is generated. After final processing, the final
output data is generated. The data store is the repository of data.

The structured approach of system design requires extensive modeling of the system.
Thus, instead of making a complete model exhibiting the functionality of system, the
DFD’s are created in a layered manner. At the first layer, the DFD is made at block
level and in lower layers, the details are shown. Thus, level “0” DFD makes a
fundamental system (Figure 2.3).

I1
Process A Output
I2

Figure 2.3: Layer 1 depiction of process A

DFD’s can represent the system at any level of abstraction. DFD of “0” level views
entire software element as a single bubble with indication of only input and output
data. Thus, “0” level DFD is also called as Context diagram. Its symbols are shown in
Figure 2.4.
Symbol Name Description

Data Flow Represents the connectivity between

various processes
Process Performs some processing of input data

External Defines source or destination of system

Entity data. The entity which receives or
supplies information.
Data Store Repository of data

Figure 2.4: Symbols of a data flow diagram

2.3.3 Rules for making DFD

The following factors should be considered while making DFDs:

1. Keep a note of all the processes and external entities. Give unique names to them.
Identify the manner in which they interact with each other.

2. Do numbering of processes.

3. Avoid complex DFDs (if possible).

4. The DFD should be internally consistent.

5. Every process should have minimum of one input and one output.
The data store should contain all the data elements that flow as input and output.
28
To understand the system functionality, a system model is developed. The developed Principles of Software
Requirements Analysis
model is used to analyze the system. The following four factors are of prime concern
for system modeling:

1. The system modeling is undertaken with some simplifying assumptions about the
system. Though these assumptions limit the quality of system model, it reduces
the system complexity and makes understanding easier. Still, the model
considers all important, critical and material factors. These assumptions are made
regarding all aspects like processes, behaviors, values of inputs etc.

2. The minute details of various components are ignored and a simplified model is
developed. For example, there may be various types of data present in the system.
The type of data having minute differences are clubbed into single category, thus
reducing overall number of data types.

3. The constraints of the system are identified. Some of them may be critical. They
are considered in modeling whereas others may be ignored. The constraints may
be because of external factors, like processing speed, storage capacity, network
features or operating system used.

4. The customers mentioned preferences about technology, tools, interfaces, design,

architecture etc. are taken care of.

Example 1: The 0th and 1st levels of DFD of Production Management System are
shown in Figure 2.5 (a) and (b)

Let us discuss the data flow diagram of Production Management System.

// Copy Figures 2.5 (a), (b)

Planning
Production Planning report
Product
PMS Finished goods
Sales
Order

Inventory
Material

Figure 2.5 (a) : Level 0 DFD of PMS

29
 Machine Code
An Overview of Process table
Software Engineering
Process type

1.0
Daily
Planning

List detail
Plan detail
Job Card 2.0
Job card table Listing Master table

3.0 Machine detail

Production

Progress table

Job Card
4.0 Acknowledgement
Material Manager
Billing
Product detail

Product detail

Figure 2.5 (b): Level 1 DFD of PMS

2.3.4 Data Dictionary

This is another tool of requirement analysis which reduces complexity of DFD. A data
dictionary is a catalog of all elements of a system. DFD depicts flow of data whereas
data dictionary gives details of that information like attribute, type of attribute, size,
names of related data items, range of values, data structure definitions etc. The name
specifies the name of attribute whose value is collected. For example, fee deposit may
be named as FD and course opted may be named as CO.

Related data items captures details of related attributes. Range of values store total
possible values of that data. Data structure definition captures the physical structure of
data items.

Some of the symbols used in data dictionary are given below:

X= [a/b] x consists of either data element a or b

X=a x consists of an optional data element a
X=a+b x consists of data element a & b.

30
 X=y{a}z x consists of some occurrences of data elements a which are Principles of Software
Requirements Analysis
between y and z.
| Separator
** Comments
@ Identifier
() Options

Example 2: The data dictionary of payroll may include the following fields:

PAYROLL = [Payroll Details]

= @ employee name + employee + id number +

employee address + Basic Salary + additional
allowances

Employee name = * name of employee *

Employee id number = * Unique identification no. given to every employee*

Basic Salary = * Basic pay of employee *

Additional allowances = * The other perks on Basic pay *

Employee name = First name + Last name

Employee address = Address 1 + Address 2 + Address 3

2.3.5 E-R Diagram

Entity-relationship (E-R) diagram is detailed logical representation of data for an

organisation. It is data oriented model of a system whereas DFD is a process oriented
model. The ER diagram represent data at rest while DFD tracks the motion of data.
ERD does not provide any information regarding functionality of data. It has three
main components – data entities, their relationships and their associated attributes.

Entity: It is most elementary thing of an organisation about which data is to be

maintained. Every entity has unique identity. It is represented by rectangular box with
the name of entity written inside (generally in capital letters).

Relationship: Entities are connected to each other by relationships. It indicates how

two entities are associated. A diamond notation with name of relationship represents
as written inside. Entity types that participate in relationship is called degree of
relationship. It can be one to one (or unary), one to many or many to many.

Cardinality & Optionally: The cardinality represents the relationship between two
entities. Consider the one to many relationship between two entities – class and
student. Here, cardinality of a relationship is the number of instances of entity student
that can be associated with each instance of entity class. This is shown in Figure 2.6.

Class Consists students

of

Figure 2.6: One to Many cardinality relationship

31
 An Overview of The minimum cardinality of a relationship is the minimum number of instances of
Software Engineering second entity (student, in this case) with each instance of first entity (class, in this
case).

In a situation where there can be no instance of second entity, then, it is called as

optional relationship. For example’ if a college does not offer a particular course then
it will be termed as optional with respect to relationship ‘offers’. This relationship is
shown in Figure 2.7.

College offers Course

Figure 2.7: Minimum cardinality relationship

When minimum cardinality of a relationship is one, then second entity is called as

mandatory participant in the relationship. The maximum cardinality is the maximum
number of instances of second entity. Thus, the modified ER diagram is shown in
Figure 2.8.

College offers Course

Figure 2.8: Modified ER diagram representing cardinalities

The relationship cardinalities are shown in Figure 2.9.

Mandatory - 1 cardinality

Mandatory many (m) cardinality, n is

n highest range

Optional 0 or 1 cardinality

Optional zero-many cardinality

Figure 2.9: Relationship cardinalities

Attributes: Attribute is a property or characteristic of an entity that is of interest to

the organisation. It is represented by oval shaped box with name of attribute written
inside it. For example, the student entity has attributes as shown in Figure 2.10.

32
 Principles of Software
Roll no. add Requirements Analysis
Name ,
Father’s name class

Student
marks

Figure 2.10: Attributes of entity student

2.3.6 Structured Requirements Definition

Structured Requirements definition is an approach to perform the study about the

complete system and its various sub-systems, the external inputs and outputs,
functionality of complete system and its various sub-systems. The following are
various steps of it:
Step 1: Make a user level data flow diagram.
This step is meant for gathering requirements with the interaction of employee. In this
process, the requirements engineer interviews each individual of organisation in order
to learn what each individual gets as input and produces as output. With this gathered
data, create separate data flow diagram for every user.
Step 2: Create combined user level data flow diagram.
Create an integrated data flow diagram by merging old data flow diagrams. Remove
the inconsistencies if encountered, in this merging process. Finally, an integrated
consistent data flow diagram is generated.
Step 3: Generate application level data flow diagram.
Perform data analysis at system’s level to define external inputs and outputs.
Step 4: Define various functionalities.
In this step, the functionalities of various sub-systems and the complete system is
defined.

) Check Your Progress 2

1) What is the advantage of DFD over ER diagram?
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
2) What is the significance specifying functional requirements in SRS document?
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
3) What is the purpose of using software metrics?

………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
33
 An Overview of
Software Engineering 2.4 SOFTWARE PROTOTYPING AND
SPECIFICATION
Prototyping is a process that enables developer to create a small model of software.
The IEEE 610.12 standard defines prototype as a preliminary form or instance of a
system that serves as a model for later stages for the final complete version of the
system.

A prototype may be categorised as follows:

1. A paper prototype, which is a model depicting human machine interaction in a

form that makes the user understand how such interaction, will occur.
2. A working prototype implementing a subset of complete features.
3. An existing program that performs all of the desired functions but additional
features are added for improvement.

Prototype is developed so that customers, users and developers can learn more about
the problem. Thus, prototype serves as a mechanism for identifying software
requirements. It allows the user to explore or criticise the proposed system before
developing a full scale system.

2.4.1 Types of Prototype

Broadly, the prototypes are developed using the following two techniques:

Throw away prototype: In this technique, the prototype is discarded once its purpose
is fulfilled and the final system is built from scratch. The prototype is built quickly to
enable the user to rapidly interact with a working system. As the prototype has to be
ultimately discarded, the attention on its speed, implementation aspects,
maintainability and fault tolerance is not paid. In requirements defining phase, a less
refined set of requirements are hurriedly defined and throw away prototype is
constructed to determine the feasibility of requirement, validate the utility of function,
uncover missing requirements, and establish utility of user interface. The duration of
prototype building should be as less as possible because its advantage exists only if
results from its use are available in timely fashion.

Evolutionary Prototype: In this, the prototype is constructed to learn about the

software problems and their solutions in successive steps. The prototype is initially
developed to satisfy few requirements. Then, gradually, the requirements are added in
the same prototype leading to the better understanding of software system. The
prototype once developed is used again and again. This process is repeated till all
requirements are embedded in this and the complete system is evolved.

According to SOMM [96] the benefits of developing prototype are listed below:

1. Communication gap between software developer and clients may be identified.

2. Missing user requirements may be unearthed.

3. Ambiguous user requirements may be depicted.

4. A small working system is quickly built to demonstrate the feasibility and

usefulness of the application to management.
34
 5. It serves as basis for writing the specification of the system. Principles of Software
Requirements Analysis
The sequence of prototyping is shown in following Figure 2.11.

Start
Requirements Quick Building Customer
Gathering Design Prototype evaluation of
prototype

Stop
Engineering product Refine Prototype

Figure 2.11: Sequence of prototyping

2.4.2 Problems of Prototyping

In some organisations, the prototyping is not as successful as anticipated. A common

problem with this approach is that people expect much from insufficient effort. As the
requirements are loosely defined, the prototype sometimes gives misleading results
about the working of software. Prototyping can have execution inefficiencies and this
may be questioned as negative aspect of prototyping. The approach of providing early
feedback to user may create the impression on user and user may carry some negative
biasing for the completely developed software also.

2.4.3 Advantages of Prototyping

The advantages of prototyping outperform the problems of prototyping. Thus, overall,

it is a beneficial approach to develop the prototype. The end user cannot demand
fulfilling of incomplete and ambiguous software needs from the developer.

One additional difficulty in adopting this approach is the large investment that exists
in software system maintenance. It requires additional planning about the
re-engineering of software. Because, it may be possible that by the time the prototype
is build and tested, the technology of software development is changed, hence
requiring a complete re-engineering of the product.

2.5 SOFTWARE METRICS

Measurement is fundamental to any engineering discipline and software engineering
is no exception. Software metric is a quantitative measure derived from the attribute
of software development life cycle [Fanton and Kaposi, 1987]. It behaves as software
measures.

A software measure is a mapping from a set of objects in the software engineering

world into a set of mathematical constructs such as numbers or vectors of numbers.

Using the software metrics, software engineer measures software processes, and the
requirements for that process. The software measures are done according to the
following parameters:

• The objective of software and problems associated with current activities,

• The cost of software required for relevant planning relative to future projects,
• Testability and maintainability of various processes and products,
• Quality of software attributes like reliability, portability and maintainability,
35
 An Overview of • Utility of software product,
Software Engineering
• User friendliness of a product.

Various characteristics of software measures identified by Basili (1989) are given

below:

• Objects of measurement: They indicate the products and processes to be

measured.
• Source of measurement: It indicates who will measure the software. For
example, software designer, software tester and software managers.
• Property of measurement: It indicates the attribute to be measured like cost of
software, reliability, maintainability, size and portability.
• Context of measurement: It indicates the environments in which context the
software measurements are applied.

Common software measures

There are significant numbers of software measures. The following are a few
common software measures:

Size : It indicates the magnitude of software system. It is most commonly used

software measure. It is indicative measure of memory requirement, maintenance
effort, and development time.

LOC : It represents the number of lines of code (LOC). It is indicative measure of

size oriented software measure. There is some standardisation on the methodology of
counting of lines. In this, the blank lines and comments are excluded. The multiple
statements present in a single line are considered as a single LOC. The lines
containing program header and declarations are counted.

) Check Your Progress 3

1) Explain rapid prototyping technique.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
2) List languages used for prototyping.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………

2.6 SUMMARY

This unit discusses various aspects of software requirements analysis, the significance
of use of engineering approach in the software design, various tools for gathering the
requirements and specifications of prototypes.

Due to the complexity involved in software development, the engineering approach is

being used in software design. Use of engineering approach in the area of
requirements analysis evolved the field of Requirements Engineering. Before the
actual system design commences, the system architecture is modeled. Entity-
relationship (E-R) diagram is detailed logical representation of data for an
36
organisation. It is data-oriented model of a system whereas DFD is a process oriented Principles of Software
Requirements Analysis
model. The ER diagram represent data at rest while DFD tracks the motion of data.
ERD does not provide any information regarding functionality of data. It has three
main components–data entities, their relationships and their associated attributes.
Structured Requirements definition is an approach to perform the study about the
complete system and its various subsystems, the external inputs and outputs,
functionality of complete system and its various subsystems. Prototyping is a process
that enables developer to create a small model of software. The IEEE 610.12 standard
defines prototype as a preliminary form or instance of a system that serves as a model
for later stages for the final complete version of the system. Measurement is
fundamental to any engineering discipline and software engineering is no exception.
Software metric is a quantitative measure derived from the attribute of software
development life cycle.

2.7 SOLUTIONS/ANSWERS

Check Your Progress 1

1) In the present era, the development of software has become very systematic and
the specification of requirements is very important. Accordingly, to analyse
requirements completely, the engineering approach is used in requirements
analysis.

Check Your Progress 2

1) The DFD presents more pictorial representation of flow of data. Moreover, by

creating different levels of DFD, the accurate and in depth understanding of data
flow is possible.

2) By specifying functional requirements, general understanding about overall

working of system is possible.

3) The purpose of using software metrics is to achieve basic objectives of the system
with low cost and high quality. Metrics provide scale for quantifying qualities and
characteristics of a software. An analogy real life is that meter is the metric of
length but to determine the length of cloth, one requires the measuring means like
meter-tape etc. Similarly, in software measurement, method must be objective and
should produce the same result independent of various measures.

Check Your Progress 3

1) Rapid prototyping techniques are used for speedy prototype development. There
are three techniques used for this purpose.

• Dynamic high level language development

• Dynamic programming
• Component and application assembly.

2) High level languages that are used for prototyping are as follows:

Java, Prolog, Small talk, Lisp etc.

37
 An Overview of
Software Engineering 2.8 FURTHER READINGS
1) Effective Requirements Practices, 2001, Ralph R. Young; Artech House
Technology Management and Professional Development Library.

2) Software Requirements and Specifications, 1995, M.Jackson; ACM Press.

3) Software Architecture in practice, 2003, Len Bass, Paul Clements, Rick Kazman;
Addison-Wesley Professional.

Reference Websites:

http://standards.ieee.org
http://www.rspa.com

38
 Software Design
UNIT 3 SOFTWARE DESIGN
Structure Page Nos.

3.0 Introduction 39
3.1 Objectives 39
3.2 Data Design 39
3.3 Architectural Design 42
3.4 Modular Design 43
3.5 Interface Design 46
3.6 Design of Human Computer Interface 49
3.7 Summary 51
3.8 Solutions/ Answers 51
3.9 Further Readings 52

3.0 INTRODUCTION
Software design is all about developing blue print for designing workable software.
The goal of software designer is to develop model that can be translated into software.
Unlike design in civil and mechanical engineering, software design is new and
evolving discipline contrary classical building design etc. In early days, software
development mostly concentrated on writing code. Software design is central to
software engineering process. Various design models are developed during design
phase. The design models are further refined to develop detailed design models which
are closely related to the program.

3. 1 OBJECTIVES
After going through this unit, you should be able to:

• design data;
• understand architectural design;
• develop modular design, and
• know the significance of Human Computer Interface.

3.2 DATA DESIGN

To learn the process of system design involved to translate user requirement to

implementable models.

• Designing of Data
• Architectural design which gives a holistic architecture of the software product
• Design of cohesive and loosely coupled module
• Design of interface and tips for good interface design
• Design of Human interface

Software Design Process

Software design is the process of applying various software engineering techniques to

develop models to define a software system, which provides sufficient details for

39
An Overview of actual realisation of the software. The goal of software design is to translate user
Software Engineering requirements into an implementable program.

Software design is the only way through which we can translate user requirements to
workable software. In contrary to designing a building software design is not a fully
developed and matured process. Nevertheless the techniques available provides us
tools for a systematic approach to the design of software. Figure 3.1 depicts the
process of software design.

Information Data design

model
User Functional
requirements model System design Code
Procedural
Requirements design

Figure 3.1 : Process of software Design

During the process of software design, the information model is translated to data
design. Functional model and behavioural model are translated to architectural design,
which defines major component of the software. Keeping in view of the importance of
design, it should be given due weightage before rushing to the coding of software.

Software design forms the foundation for implementation of a software system and
helps in the maintenance of software in future too. Software quality and software
design process are highly interrelated. Quality is built into the software during the
design phase.

High level design gives a holistic view of the software to be built, where as low level
refinements of the design are very closely related to the final source code. A good
design can make the work of programmer easy and hardly allow the programmer to
forget the required details. Sufficient time should be devoted to design process to
ensure good quality software.

The following are some of the fundamentals of design:

• The design should follow a hierarchical organisation.

• Design should be modular which are logically partitioned into modules which
are relatively independent and perform independent task.
• Design leading to interface that facilitate interaction with external environment.
• Step wise refinement to more detailed design which provides necessary details
for the developer of code.
• Modularity is encouraged to facilitate parallel development, but, at the same
time, too many modules lead to the increase of effort involved in integrating the
modules.

Data design is the first and the foremost activity of system Design. Before going into
the details of data design, let us discuss what is data? Data describes a real-world
information resource that is important for the application. Data describes various
entities like customer, people, asset, student records etc.
Identifying data in system design is an iterative process. At the highest level, data is
defined in a very vague manner. A high level design describes how the application
handles these information resources. As we go into more details, we focus more on
the types of data and it’s properties. As you keep expanding the application to the
business needs or business processes, we tend to focus more on the details.

40
 Data design Software Design

Architectural design

Modular Design

Human Computer Interface Design

Figure 3.2 : Technical aspects of design

The primary objective of data design is to select logical representation of data items
identified in requirement analysis phase. Figure 3.2 depicts the technical aspects of
design. As we begin documenting the data requirements for the application, the
description for each item of data typically include the following:
• Name of the data item
• General description of the data item
• Characteristics of data item
• Ownership of the data item
• Logical events, processes, and relationships.

Data Sructure

A data structure defines a logical relationship between individual elements of a group

of data. We must understand the fact that the structure of information affects the
design of procedures/algorithms. Proper selection of data structure is very important
in data designing. Simple data structure like a scalar item forms the building block of
more sophisticated and complex data structures.

A scalar item is the simplest form of data. For example, January (Name of the Month),
where as the collection of months in a year form a data structure called a vector item.

Example:

Month as string

months_in_year = [Jan, …, Dec]

The items in the vector called array is sequenced and index in a manner so as to retive
particular element in the arry.

Month_in_year[4] will retrieve Apr

The vector items are in contiguous memory locations in the computer memory. There
are other variety of lists which are non-contiguously stored. These are called linked
lists. There are other types of data structures known as hierarchical data structure such
as tree. Trees are implemented through linked lists.

) Check Your Progress 1

1) Quality is built into the software during the design phase explain?
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
41
An Overview of 2) Structure of information effects the design of algorithm. True False
Software Engineering
3) Design form the foundation of Software Engineering, Explain?
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………

3.3 ARCHITECTURAL DESIGN

The objective of architectural design is to develop a model of software architecture
which gives a overall organisation of program module in the software product.
Software architecture encompasses two aspects of structure of the data and
hierarchical structure of the software components. Let us see how a single problem
can be translated to a collection of solution domains (refer to Figure 3.3).

S1 S2 S5
Problem
S1 S2 S5
S3 S4 S6

S3 S4

S6

Figure 3.3: Problem, Solutions and Architecture

Architectural design defines organisation of program components. It does not provide

the details of each components and its implementation. Figure 3.4 depicts the
architecture of a Financial Accounting System.

Financial Accounting
Management System

Fixed Asset
Accounts Management Sundry Debtors
Receivable System System

Figure 3.4: Architecture of a financial accounting system

The objective of architectural design is also to control relationship between modules.

One module may control another module or may be controlled by another module.
These characteristics are defined by the fan-in and fan-out of a particular module. The
organisation of module can be represented through a tree like structure.

42
Let us consider the following architecture of a software system. Software Design

The number of level of component in the structure is called depth and the number of
component across the horizontal section is called width. The number of components
which controls a said component is called fan-in i.e., the number of incoming edges to
a component. The number of components that are controlled by the module is called
fan-out i.e., the number of outgoing edges.

S0 S1 S5

S1 S2 S5 S2

Figure 3.5: Fan-in and Fan-out

S0 controls three components, hence the fan-out is 3. S2 is controlled by two

components, namely, S1 and S2, hence the fan-in is 2 (refer to Figure 3.5).

Figure 3.6 : Typical architecture of a system

The architectural design provides holistic picture of the software architecture and
connectivity between different program components (refer to Figure 3.6).

3.4 MODULAR DESIGN

Modular design facilitates future maintenance of software. Modular design have
become well accepted approach to built software product.

Software can be divided in to relatively independent, named and addressable

component called a module. Modularity is the only attribute of a software product that
makes it manageable and maintainable. The concept of modular approach has been
derived from the fundamental concept of “divide and conquer”. Dividing the software
to modules helps software developer to work on independent modules that can be later
integrated to build the final product. In a sense, it encourages parallel development
effort thus saving time and cost.
43
An Overview of During designing of software one must keep a balance between number of modules
Software Engineering and integration cost. Although, more numbers of modules make the software product
more manageable and maintainable at the same time, as the number of modules
increases, the cost of integrating the modules also increases.

Modules are generally activated by a reference or through a external system interrupt.

Activation starts life of an module. A module can be classified three types depending
activation mechanism.

• An incremental module is activated by an interruption and can be interrupted by

another interrupt during the execution prior to completion.

• A sequential module is a module that is referenced by another module and without

interruption of any external software.

• Parallel module are executed in parallel with another module

Sequential module is most common type of software module. While modularity is

good for software quality, independence between various module are even better for
software quality and manageability. Independence is a measured by two parameters
called cohesion and coupling.

Cohesion is a measure of functional strength of a software module. This is the degree

of interaction between statements in a module. Highly cohesive system requires little
interaction with external module.

Coupling is a measure of interdependence between/among modules. This is a measure

of degree of interaction between module i.e., their inter relationship.

Hence, highly cohesive modules are desirable. But, highly coupled modules are
undesirable (refer to Figure 3.7 and Figure 3.8).

Cohesion

Cohesiveness measure functional relationship of elements in a module. An element

could be a instruction, a group of instructions, data definitions or reference to another
module.

Cohesion tells us how efficiently we have positioned our system to modules. It may be
noted that modules with good cohesion requires minimum coupling with other
module.

Low cohesion High cohesion

Undesirable Desirable

Figure 3.7 : Cohesion

There are several types of cohesion arranged from bad to best.

• Coincidental : This is worst form of cohesion, where a module performs a

number of unrelated task.
• Logical : Modules perform series of action, but are selected by a calling module.

• Procedural : Modules perform a series of steps. The elements in the module must
takeup single control sequence and must be executed in a specific order.

44
• Communicational : All elements in the module is executed on the same data set Software Design
and produces same output data set.

• Sequential : Output from one element is input to some other element in the
module. Such modules operates on same data structure.

• Functional : Modules contain elements that perform exactly one function.

The following are the disadvantages of low cohesion:

• Difficult to maintain
• Tends to depend on other module to perform certain tasks
• Difficult to understand.

Coupling

In computer science, coupling is defined as degree to which a module interacts and

communicates with another module to perform certain task. If one module relies on
another the coupling is said to be high. Low level of coupling means a module doses
not have to get concerned with the internal details of another module and interact with
another module only with a suitable interface.

Loosely coupled Tightly coupled

Desirable Undesirable

Figure 3.8 : Coupling

The types of coupling from best (lowest level of coupling) to worst (high level of
coupling) are described below:

• Data coupling: Modules interact through parameters.

Module X passes parameter A to module Y

• Stamp coupling: Modules shares composite data structure.

• Control coupling: One module control logic flow of another module. For
example, passing a flag to another module which determines the sequence of
action to be performed in the other module depending on the value of flag such as
true or false.

• External coupling: Modules shares external data format. Mostly used in

communication protocols and device interfaces

• Common coupling: Modules shares the same global data.

• Content coupling: One module modifies the data of another module.

Coupling and cohesion are in contrast to each other. High cohesion often correlates
with low coupling and vice versa.

In computer science, we strive for low-coupling and high cohesive modules.

The following are the disadvantages of high coupling:

• Ripple effect.
• Difficult to reuse. Dependent modules must be included.
• Difficult to understand the function of a module in isolation.
45
An Overview of Figure 3.9 depicts highly cohesive and loosely coupled system. Figure 3.10 depicts a
Software Engineering low cohesive and tightly coupled system.

Figure 3.9 : High cohesive and loosely coupled system (desirable)

Figure 3.10 : Low cohesive and tightly coupled system (undesirable)

) Check Your Progress 2

1) Content coupling is a low level coupling True False

2) Modules sharing global data refer to ____________.

3) Which is the best form of cohesion?

………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………

3.5 INTERFACE DESIGN

Interface design deals with the personnel issues of the software. Interface design is
one of the most important part of software design. It is crucial in a sense that user
interaction with the system takes place through various interfaces provided by the
software product.
46
Think of the days of text based system where user had to type command on the Software Design
command line to execute a simple task.

Example of a command line interface:

• run prog1.exe /i=2 message=on

The above command line interface executes a program prog1.exe with a input i=2
with message during execution set to on. Although such command line interface gives
liberty to the user to run a program with a concise command. It is difficult for a novice
user and is error prone. This also requires the user to remember the command for
executing various commands with various details of options as shown above.

Example of Menu with option being asked from the user (refer to Figure 3.11).

To run the program select the

option below

1. Option 1
2. Option 2
3. Option 3
4. Back
5. Exit program

Enter your option ____

Figure 3.11 : A menu based interface

This simple menu allow the user to execute the program with option available as a
selection and further have option for exiting the program and going back to previous
screen. Although it provide grater flexibility than command line option and does not
need the user to remember the command still user can’t navigate to the desired option
from this screen. At best user can go back to the previous screen to select a different
option.

Modern graphical user interface provides tools for easy navigation and interactivity to
the user to perform different tasks.

The following are the advantages of a Graphical User Interface (GUI):

• Various information can be display and allow user to switch to different task
directly from the present screen.
• Useful graphical icons and pull down menu reduces typing effort by the user.
• Provides key-board shortcut to perform frequently performed tasks.
• Simultaneous operations of various task without loosing the present context.

Any interface design is targeted to users of different categories.

• Expert user with adequate knowledge of the system and application

• Average user with reasonable knowledge
• Novice user with little or no knowledge.

The following are the elements of good interface design:

• Goal and the intension of task must be identified.

47
An Overview of • The important thing about designing interfaces is all about maintaining
Software Engineering consistency. Use of consistent color scheme, message and terminologies helps.

• Develop standards for good interface design and stick to it.

• Use icons where ever possible to provide appropriate message.

• Allow user to undo the current command. This helps in undoing mistake
committed by the user.

• Provide context sensitive help to guide the user.

• Use proper navigational scheme for easy navigation within the application.

• Discuss with the current user to improve the interface.

• Think from user prospective.

• The text appearing on the screen are primary source of information exchange
between the user and the system. Avoid using abbreviation. Be very specific in
communicating the mistake to the user. If possible provide the reason for error.

• Navigation within the screen is important and is specially useful for data entry
screen where keyboard is used intensively to input data.

• Use of color should be of secondary importance. It may be kept in mind about

user accessing application in a monochrome screen.

• Expect the user to make mistake and provide appropriate measure to handle such
errors through proper interface design.

• Grouping of data element is important. Group related data items accordingly.

• Justify the data items.

• Avoid high density screen layout. Keep significant amount of screen blank.

• Make sure an accidental double click instead of a single click may does some
thing unexpected.

• Provide file browser. Do not expect the user to remember the path of the required
file.

• Provide key-board shortcut for frequently done tasks. This saves time.

• Provide on-line manual to help user in operating the software.

• Always allow a way out (i.e., cancellation of action already completed).

• Warn user about critical task, like deletion of file, updating of critical information.

• Programmers are not always good interface designer. Take help of expert
professional who understands human perception better than programmers.

• Include all possible features in the application even if the feature is available in
the operating system.

48
• Word the message carefully in a user understandable manner. Software Design

• Develop navigational procedure prior to developing the user interface.

3.6 DESIGN OF HUMAN COMPUTER

INTERFACE
Human Computer Interface (HCI) design is topic that is gaining significance as the
use of computers is growing. Let us look at a personal desktop PC that has following
interface for humans to interact.
• A key board
• A Computer Mouse
• A Touch Screen (if equipped with)
• A program on your Windows machine that includes a trash can, icons of various
programs, disk drives, and folders

System Model/ Interface design User model of the

Design model system

Figure 3.12: The process of interface design

What do these things have in common? These are all human-computer interfaces
which were designed to make it easier to accomplish things with a computer. If we
recall the early days computer, some one had to remember long cryptic strings of
commands in accomplish simplest to simplest thing with a computer like coping a file
from one folder to another or deleting a file etc. It is due to the evolution of human-
computer interface and human-computer interface designers that’s now being
accomplished with the click of a mouse.

The overall process of design leads to the translation of design models to user model.
Human-Computer Interface design goal is to discover the most efficient way to design
interfaces for human interaction and understandable electronic messages. A lot of
research is taking place in this area that even helps physically disabled person to
operate computer as easily as a normal person. Figure 3.12 depicts the process of
interface design.

A branch of computer science is devoted to this area, with recommendations for the
proper design of menus, icons, forms, messages, dialogue as well as data display. The
user friendliness of the program we are using is a result of interface design. The
buttons, pull down menu, context sensitive help have been designed to make it easy
for you to access the program.

The process of HCI design begins with the a creation of a model of system function as
perceived by the end user. These models are designed by delineating them from
design issues and program structure. HCI establishes a user model of the overall
system.

The following are some of the principles of Good Human computer interface design:

Diversity: Consider the types of user frequently use the system. The designer must
consider the types of users ranging from novice user, knowledgeable but intermittent
49
An Overview of user and expert frequent user. Accommodating expectation of all types of user is
Software Engineering important. Each type of user expects the screen layout to accommodate their desires,
novices needing extensive help where as expert user want to accomplish the task in
quickest possible time.

For example providing a command such as ^P (control P) to print a specific report as

well as a printer icon to do the same job for the novice user.
Rules for Human Computer Interface Design:
1. Consistency :
o Interface is deigned so as to ensure consistent sequences of actions for
similar situations. Terminology should be used in prompts, menus, and
help screens should be identical. Color scheme, layout and fonts should
be consistently applied throughout the system.
2. Enable expert users to use shortcuts:
o Use of short cut increases productivity. Short cut to increase the pace of
interaction with use of, special keys and hidden commands.
3. Informative feedback :
o The feedback should be informative and clear.
4. Error prevention and handling common errors :
o Screen design should be such that users are unlikely to make a serious
error. Highlight only actions relevant to current context. Allowing user
to select options rather than filling up details. Don’t allow alphabetic
characters in numeric fields
o In case of error, it should allow user to undo and offer simple,
constructive, and specific instructions for recovery.
5 Allow reversal of action : Allow user to reverse action committed. Allow user to
migrate to previous screen.
6. Reduce effort of memorisation by the user :
o Do not expect user to remember information. A human mind can
remember little information in short term memory. Reduce short term
memory load by designing screens by providing options clearly using
pull-down menus and icons
7. Relevance of information : The information displayed should be relevant to the
present context of performing certain task.
8. Screen size: Consideration for screen size available to display the information.
Try to accommodate selected information in case of limited size of the window.
9. Minimize data input action : Wherever possible, provide predefined selectable
data inputs.
10. Help : Provide help for all input actions explaining details about the type of input
expected by the system with example.
About Errors: Some errors are preventable. Prevent errors whenever possible. Steps
can be taken so that errors are less likely to occur, using methods such as organising
screens and menus functionally, designing screens to be distinctive and making it
difficult for users to commit irreversible actions. Expect users to make errors, try to
anticipate where they will go wrong and design with those actions in mind.
Norman’s Research
Norman D. A. has contributed extensively to the field of human-computer interface
design. This psychologist has taken insights from the field of industrial product design
and applied them to the design of user interfaces.
According to Norman, design should use both knowledge in the world and knowledge
in the head. Knowledge in the world is overt–we don’t have to overload our short term
50
memory by having to remember too many things (icons, buttons and menus provide Software Design
us with knowledge in the world. The following are the mappings to be done:

• Mapping between actions and the resulting effect.

• Mapping between the information that is visible and the interpretation of the
system state. For example, it should be obvious what the function of a button or
menu is. Do not try to built your own meaning to the commonly used icons
instead use conventions already established for it. Never use a search icon to print
a page.

• Hyperlink should be used to migrate from one page to connected page.

) Check Your Progress 3

1) Keyboard short-cut is used to perform __________.

2) What are the types of user errors you may anticipate while designing a user
interface. Explain?
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………

3.7 SUMMARY

Design is a process of translating analysis model to design models that are further
refined to produce detailed design models. The process of refinement is the process of
elaboration to provides necessary details to the programmer. Data design deals with
data structure selection and design. Modularity of program increases maintainability
and encourages parallel development. The aim of good modular design is to produce
highly cohesive and loosely coupled modules. Independence among modules is
central to modularity. Good user interface design helps software to interact effectively
to external environment. Tips for good interface design helps designer to achieve
effective user interface.

Quality is built into software during the design of software. The final word is: Design
process should be given due weightage before rushing for coding.

3.8 SOLUTIONS/ANSWERS

Check Your Progress 1

1) In building a design, where the quality of structural strength and other aspects
are determined by the design of the building. In software design, the design
process goes through a series of refinement process and reviews, to see whether
the user requirements and other quality parameters are properly not reflected in
the design model. A good design is more likely to deliver good software. The
process of getting it right starts from the software design stage.
• Data design affects the efficiency of algorithms.
• Modularity enables the software component to perform distinct
independent tasks with little chance of propagating errors to other
module.
• Good interface design minimizes user errors and increases user
friendliness of the system.
51
An Overview of 2) True.
Software Engineering
3) Software design is the first step of translating user requirement to technical
domain of software development. Without designing there is always a risk of
designing an unstable system. Without design we can’t review the requirements of
the product until it is delivered to the user. Design helps in future maintenance of
the system.

Check Your Progress 2

1) False
2) Common coupling
3) Functional.

Check your Progress 3

1) Frequently performed tasks.

2) Anticipation user error provides vital input for user interface design. Prevent
errors wherever possible and steps can be taken to design interface such that
errors are less likely to occur. The methods that may be adopted may include well
organisation of screen and menus functionally. Using user understandable
language, designing screens to be distinctive and making it difficult for users to
commit irreversible actions. Provide user confirmation to critical actions.
Anticipate where user can go wrong and design the interface keeping this in mind.

3.9 FURTHER READINGS

1) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson

Education.
2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman;
McGraw-Hill International Edition.
3) Software Design : From Programming to Architecture, First Eition, 2003, Eric
J. Braude; Wiley

Reference Websites

http://www.ieee.org
http://www.rspa.com
http://sdg.csail.mit.edu

52
 Software Testing
UNIT 4 SOFTWARE TESTING
Structure Page Nos.
4.0 Introduction 53
4.1 Objectives 54
4.2 Basic Terms used in Testing 54
4.2.1 Input Domain
4.2.2 Black Box and White Box testing Strategies
4.2.3 Cyclomatic Complexity
4.3 Testing Activities 64
4.4 Debugging 65
4.5 Testing Tools 67
4.6 Summary 68
4.7 Solutions/Answers 69
4.8 Further Readings 69

4.0 INTRODUCTION
Testing means executing a program in order to understand its behaviour, that is,
whether or not the program exhibits a failure, its response time or throughput for
certain data sets, its mean time to failure, or the speed and accuracy with which users
complete their designated tasks. In other words, it is a process of operating a system or
component under specified conditions, observing or recording the results, and making
an evaluation of some aspect of the system or component. Testing can also be
described as part of the process of Validation and Verification.
Validation is the process of evaluating a system or component during or at the end of
the development process to determine if it satisfies the requirements of the system, or,
in other words, are we building the correct system?
Verification is the process of evaluating a system or component at the end of a phase
to determine if it satisfies the conditions imposed at the start of that phase, or, in other
words, are we building the system correctly?
Software testing gives an important set of methods that can be used to evaluate and
assure that a program or system meets its non-functional requirements.
To be more specific, software testing means that executing a program or its
components in order to assure:
• The correctness of software with respect to requirements or intent;
• The performance of software under various conditions;
• The robustness of software, that is, its ability to handle erroneous inputs and
unanticipated conditions;
• The usability of software under various conditions;
• The reliability, availability, survivability or other dependability measures of
software; or
• Installability and other facets of a software release.
The purpose of testing is to show that the program has errors. The aim of most testing
methods is to systematically and actively locate faults in the program and repair them.
Debugging is the next stage of testing. Debugging is the activity of:
• Determining the exact nature and location of the suspected error within
the program and
• Fixing the error. Usually, debugging begins with some indication of the
existence of an error.
The purpose of debugging is to locate errors and fix them.

53
An Overview of
Software Engineering 4.1 OBJECTIVES

After going through this unit, you should be able to:

• know the basic terms using in testing terminology;
• black box and White box testing techniques;
• other testing techniques; and
• some testing tools.

4.2 BASIC TERMS USED IN TESTING

Failure: A failure occurs when there is a deviation of the observed behavior of a
program, or system, from its specification. A failure can also occur if the observed
behaviour of a system, or program, deviates from its intended behavior.
Fault: A fault is an incorrect step, process, or data definition in a computer program.
Faults are the source of failures. In normal language, software faults are usually
referred to as “bugs”.
Error: The difference between a computed, observed, or measured value or condition
and the true, specified, or theoretically correct value or condition.
Test Cases: Ultimately, testing comes down to selecting and executing test cases. A
test case for a specific component consists of three essential pieces of information:
• A set of test inputs;
• The expected results when the inputs are executed; and
• The execution conditions or environments in which the inputs are to be
executed.

Some Testing Laws

• Testing can only be used to show the presence of errors, but never the absence
or errors.
• A combination of different verification & validation (V&V) methods outprform
any single method alone.
• Developers are unsuited to test their own code.
• Approximately 80% of the errors are found in 20% of the code.
• Partition testing, that is, methods that partition the input domain or the program
and test according to those partitions. This is better than random testing.
• The adequacy of a test suite for coverage criterion can only be defined
intuitively.
4.2.1 Input Domain
To conduct an analysis of the input, the sets of values making up the input domain are
required. There are essentially two sources for the input domain. They are:

1. The software requirements specification in the case of black box testing

method; and
2. The design and externally accessible program variables in the case of
white box testing.
In the case of white box testing, input domain can be constructed from the following
sources.

• Inputs passed in as parameters; Variables that are inputs to function under test
can be: (i) Structured data such as linked lists, files or trees, as well as atomic
data such as integers and floating point numbers;

54
(ii) A reference or a value parameter as in the C function declaration Software Testing
int P(int *power, int base) {
...}
• Inputs entered by the user via the program interface;
• Inputs that are read in from files;
• Inputs that are constants and precomputed values; Constants declared in an
enclosing scope of function under test, for example,
#define PI 3.14159
double circumference(double radius)
{
return 2*PI*radius;
}
In general, the inputs to a program or a function are stored in program variables. A
program variable may be:
• A variable declared in a program as in the C declarations
For example: int base; char s[];
• Resulting from a read statement or similar interaction with the environment,
For example: scanf(‘‘%d\n’’, &x);

4.2.2 Black Box and White Box Test Case Selection Strategies
• Black box Testing: In this method, where test cases are derived from the
functional specification of the system; and
• White box Testing: In this method, where test cases are derived from the
internal design specifications or actual code (Sometimes referred to as Glass-
box).
Black box test case selection can be done without any reference to the program design
or the program code. Test case selection is only concerned with the functionality and
features of the system but not with its internal operations.

• The real advantage of black box test case selection is that it can be done before
the design or coding of a program. Black box test cases can also help to get the
design and coding correct with respect to the specification. Black box testing
methods are good at testing for missing functions or program behavior that
deviates from the specification. Black box testing is ideal for evaluating
products that you intend to use in your systems.

• The main disadvantage of black box testing is that black box test cases cannot
detect additional functions or features that have been added to the code. This is
especially important for systems that need to be safe (additional code may
interfere with the safety of the system) or secure (additional code may be used
to break security).
White box test cases are selected using the specification, design and code of the
program or functions under test. This means that the testing team needs access to the
internal designs or code for the program.

• The chief advantage of white box testing is that it tests the internal details of the
code and tries to check all the paths that a program can execute to determine if a
problem occurs. White box testing can check additional functions or code that
has been implemented, but not specified.

• The main disadvantage of white box testing is that you must wait until after
design and coding of the programs of functions under test have been completed
in order to select test cases.

55
An Overview of Methods for Black box testing strategies
Software Engineering
A number of test case selection methods exist within the broad classification of black
box and white box testing.
For Black box testing strategies, the following are the methods:
• Boundary-value Analysis;
• Equivalence Partitioning.
We will also study State Based Testing, which can be classified as opaque box
selection strategies that is somewhere between black box and white box selection
strategies.

Boundary-value-analysis
The basic concept used in Boundary-value-analysis is that if the specific test cases are
designed to check the boundaries of the input domain then the probability of detecting
an error will increase. If we want to test a program written as a function F with two
input variables x and y., then these input variables are defined with some boundaries
like a1 ≤ x ≤ a2 and b1 ≤ y ≤ b2. It means that inputs x and y are bounded by two
intervals [a1, a2] and [b1, b2].

Test Case Selection Guidelines for Boundary Value Analysis

The following set of guidelines is for the selection of test cases according to the
principles of boundary value analysis. The guidelines do not constitute a firm set of
rules for every case. You will need to develop some judgement in applying these
guidelines.

1. If an input condition specifies a range of values, then construct valid test cases
for the ends of the range, and invalid input test cases for input points just
beyond the ends of the range.
2. If an input condition specifies a number of values, construct test cases for the
minimum and maximum values; and one beneath and beyond these values.
3. If an output condition specifies a range of values, then construct valid test cases
for the ends of the output range, and invalid input test cases for situations just
beyond the ends of the output range.
4. If an output condition specifies a number of values, construct test cases for the
minimum and maximum values; and one beneath and beyond these values.
5. If the input or output of a program is an ordered set (e.g., a sequential file, linear
list, table), focus attention on the first and last elements of the set.

Example 1: Boundary Value Analysis for the Triangle Program

Consider a simple program to classify a triangle. Its input consists of three positive
integers (say x, y, z) and the data types for input parameters ensures that these will be
integers greater than zero and less than or equal to 100. The three values are
interpreted as representing the lengths of the sides of a triangle. The program then
prints a message to the standard output that states whether the triangle, if it can be
formed, is scalene, isosceles, equilateral, or right-angled.
Solution: Following possible boundary conditions are formed:
1. Given sides (A; B; C) for a scalene triangle, the sum of any two sides is greater
than the third and so, we have boundary conditions A + B > C, B + C > A and A
+ C > B.
2. Given sides (A; B; C) for an isosceles triangle two sides must be equal and so
we have boundary conditions A = B, B = C or A = C.
3. Continuing in the same way for an equilateral triangle the sides must all be of
equal length and we have only one boundary where A = B = C.
4. For right-angled triangles, we must have A2+B2 = C2.
56
On the basis of the above boundary conditions, test cases are designed as follows Software Testing
(Table 4.1):
Table 4.1: Test cases for Example-1

Test case x y z Expected Output

1 100 100 100 Equilateral triangle
2 50 3 50 Isosceles triangle
3 40 50 40 Equilateral triangle
4 3 4 5 Right-angled triangles
5 10 10 10 Equilateral triangle
6 2 2 5 Isosceles triangle
7 100 50 100 Scalene triangle
8 1 2 3 Non-triangles
9 2 3 4 Scalene triangle
10 1 3 1 Isosceles triangle

Equivalence Partitioning
Equivalence Partitioning is a method for selecting test cases based on a partitioning of
the input domain. The aim of equivalence partitioning is to divide the input domain of
the program or module into classes (sets) of test cases that have a similar effect on the
program. The classes are called Equivalence classes.
Equivalence Classes
An Equivalence Class is a set of inputs that the program treats identically when the
program is tested. In other words, a test input taken from an equivalence class is
representative of all of the test inputs taken from that class. Equivalence classes are
determined from the specification of a program or module. Each equivalence class is
used to represent certain conditions (or predicates) on the input domain. For
equivalence partitioning it is usual to also consider valid and invalid inputs. The terms
input condition, valid and invalid inputs, are not used consistently. But, the following
definition spells out how we will use them in this subject. An input condition on the
input domain is a predicate over the values of the input domain. A Valid input to a
program or module is an element of the input domain that is expected to return a non-
error value. An Invalid input is an input that is expected to return an error value.
Equivalence partitioning is then a systematic method for identifying interesting input
conditions to be tested. An input condition can be applied to a set of values of a
specific input variable, or a set of input variables
as well.
A Method for Choosing Equivalence Classes
The aim is to minimize the number of test cases required to cover all of the identified
equivalence classes. The following are two distinct steps in achieving this goal:
Step 1: Identify the equivalence classes
If an input condition specifies a range of values, then identify one valid equivalence
class and two invalid equivalence classes.
For example, if an input condition specifies a range of values from 1 to 99, then, three
equivalence classes can be identified:
• One valid equivalence class: 1< X < 99
• Two invalid equivalence classes X < 1 and X > 99
Step 2: Choose test cases
The next step is to generate test cases using the equivalence classes identified in the
previous step. The guideline is to choose test cases on the boundaries of partitions and
test cases close to the midpoint of the partition. In general, the idea is to select at least
one element from each equivalence class.

57
An Overview of Example 2: Selecting Test Cases for the Triangle Program
Software Engineering
In this example, we will select a set of test cases for the following triangle program
based on its specification. Consider the following informal specification for the
Triangle Classification Program. The program reads three integer values from the
standard input. The three values are interpreted as representing the lengths of the sides
of a triangle. The program then prints a message to the standard output that states
whether the triangle, if it can be formed, is scalene, isosceles, equilateral, or right-
angled. The specification of the triangle classification program lists a number of
inputs for the program as well as the form of output. Further, we require that each of
the inputs “must be” a positive integer. Now, we can determine valid and invalid
equivalence classes for the input conditions. Here, we have a range of values. If the
three integers we have called x, y and z are all greater than zero, then, they are valid
and we have the equivalence class.
ECvalid = f(x,y, z) x > 0 and y > 0 and z > 0.
For the invalid classes, we need to consider the case where each of the three variables
in turn can be negative and so we have the following equivalence classes:
ECInvalid1 = f(x, y, z) x < 0 and y > 0 and z > 0
ECInvalid2 = f(x, y, z) x > 0 and y <0 and z > 0
ECInvalid3 = f(x, y, z) x > 0 and y > 0 and z < 0
Note that we can combine the valid equivalence classes. But, we are not allowed to
combine the invalid equivalence classes. The output domain consists of the text
‘strings’ ‘isosceles’, ‘scalene’, ‘equilateral’ and ‘right-angled’. Now, different values
in the input domain map to different elements of the output domain to get the
equivalence classes in Table 4.2. According to the equivalence partitioning method we
only need to choose one element from each of the classes above in order to test the
triangle program.

Table 4.2: The equivalence classes for the triangle program

Equivalence class Test Inputs Expected Outputs

ECscalene f(3, 5, 7), . . . g “Scalene”
ECisosceles f(2, 3, 3), . . . g f(2, 3, 3), . . g “Isosceles”
ECequilateral f(7, 7, 7), . . . g f(7, 7, 7), . . . g “Equilateral”
ECright angled f(3, 4, 5), . . . “Right Angled”
ECnon _ triangle f(1, 1, 3), . . . “Not a Triangle”
ECinvalid1 f(-1, 2, 3), (0, 1, 3), . . . “Error Value”
ECinavlid2 f(1, -2, 3), (1, 0, 3), . . . “Error Value”
ECinavlid3 f(1, 2, -3), (1, 2, 0),. . . “Error Value”

Methods for White box testing strategies

In this approach, complete knowledge about the internal structure of the source code
is required. For White-box testing strategies, the methods are:
1. Coverage Based Testing
2. Cyclomatic Complexity
3. Mutation Testing
Coverage based testing
The aim of coverage based testing methods is to ’cover’ the program with test cases
that satisfy some fixed coverage criteria. Put another way, we choose test cases to
exercise as much of the program as possible according to some criteria.
Coverage Based Testing Criteria
Coverage based testing works by choosing test cases according to well-defined
‘coverage’ criteria. The more common coverage criteria are the following.

58
• Statement Coverage or Node Coverage: Every statement of the program Software Testing
should be exercised at least once.
• Branch Coverage or Decision Coverage: Every possible alternative in a
branch or decision of the program should be exercised at least once. For if
statements, this means that the branch must be made to take on the values true
or false.
• Decision/Condition Coverage: Each condition in a branch is made to evaluate
to both true and false and each branch is made to evaluate to both true and false.
• Multiple condition coverage: All possible combinations of condition outcomes
within each branch should be exercised at least once.
• Path coverage: Every execution path of the program should be exercised at
least once.
In this section, we will use the control flow graph to choose white box test cases
according to the criteria above. To motivate the selection of test cases, consider the
simple program given in Program 4.1.
Example 3:
void main(void)
{
int x1, x2, x3;
scanf("%d %d %d", &x1, &x2, &x3);
if ((x1 > 1) && (x2 == 0))
x3 = x3 / x1;
if ((x1 == 2) || (x3 > 1))
x3 = x3 + 1;
while (x1 >= 2)
x1 = x1 - 2;
printf("%d %d %d", x1, x2, x3);
}

Program 4.1: A simple program for white box testing

The first step in the analysis is to generate the flow chart, which is given in Figure 4.1.
Now what is needed for statement coverage? If all of the branches are true, at least
once, we will have executed every statement in the flow chart. Put another way to
execute every statement at least once, we must execute the path ABCDEFGF. Now,
looking at the conditions inside each of the three branches, we derive a set of
constraints on the values of x1, x2 and x3 such that all the three branches are
extended. A test case of the form (x1; x2; x3) = (2; 0; 3) will execute all of the
statements in the program.
Note that we need not make every branch evaluate to true and false, nor have we make
every condition evaluate to true and false, nor we traverse every path in the program.

To make the first branch true, we have test input (2; 0; 3) that will make all of the
branches true. We need a test input that will now make each one false. Again looking
at all of the conditions, the test input (1; 1; 1) will make all of the branches false.

For any of the criteria involving condition coverage, we need to look at each of the
five conditions in the program: C1 = (x1>1), C2 = (x2 == 0), C3 = (x1 == 2), C4 =
(x3>1) and C5 = (x1 >= 2). The test input (1; 0; 3) will make C 1 false, C2 true, C3
false, C4 true and C5 false.
Examples of sets of test inputs and the criteria that they meet are given in Table 4.3.
The set of test cases meeting the multiple condition criteria is given in Table 4.4. In
the table, we let the branches B1 = C1&&C2, B2 = C3||C4 and B3 = C5.
59
An Overview of Start
Software Engineering

int x1,x2,x3
scanf("%d %d %d", &x1, &x2, & A
x3)

True x3 = x3/x1
(x1>1) && C
(x2==0)

False

True
(x1==2) ||
(x3 >1) x3 = x3+1;
E

False

x1>= 2
True x1 = x1 - 2; G

False

End

Figure 4.1: The flow chart for the program 4.1

Table 4.3: Test cases for the various coverage criteria for the program 4.1

Coverage Criteria Test Inputs (x1, x2, x3) Execution Paths

Statement (2, 0, 3) ABCDEFGF

(2, 0, 3), ABCDEFGF
Branch (1, 1, 1) ABDF
Condition (1, 0, 3), ABDEF
(2, 1, 1) ABDFGF
Decision/ Condition (2, 0, 4), ABCDEFGF
(1, 1, 1) ABDF

Multiple Condition (2, 0, 4), ABCDEFGF

(2, 1, 1), ABDEFGF
(1, 0, 2), ABDEF
(1, 1, 1) ABDF
Path (2, 0, 4), ABCDEFGF
(2, 1, 1), ABDFGF
(1, 0, 2), ABDEF
(4, 0, 0), ABCDFGFGF

60
 Table 4.4: Multiple condition coverage for the program in Figure 4.1 Software Testing

Test C1 C2 C3 C4 B2 B3
cases x1 > 1 x2==0 B1 x1==2 x3 > 1 C5
x1 ≥ 2
(1,0,3) F T F F T T F
(2,1,1) T F F T F F T
(2,0,4) T T T T T T T
(1,1,1) F F F F F F F
(2,0,4) T T T T T T T
(2,1,1) T F F T F T T
(1,0,2) F T F F T T F
(1,1,1) F F F F F F F

4.2.3 Cyclomatic Complexity

Control flow graph (CFG)
A control flow graph describes the sequence in which different instructions of a
program get executed. It also describes how the flow of control passes through the
program. In order to draw the control flow graph of a program, we need to first
number all the statements of a program. The different numbered statements serve as
nodes of the control flow graph. An edge from one node to another node exists if the
execution of the statement representing the first node can result in the transfer of
control to the other node. Following structured programming constructs are
represented as CFG:

Figure 4.2 : sequence Figure 4.3 : if -else

Figure 4.4 : while-loop Figure 4.5: case

Example 4.4: Draw CFG for the program given below.

int sample (a,b)
int a,b;
{
1 while (a!= b) {
2 if (a > b)
3 a = a-b;
4 else b = b-a;}
5 return a;
}

61
An Overview of Program 4.2: A program
Software Engineering
In the above program, two control constructs are used, namely, while-loop and
if-then-else. A complete CFG for the program of Program 4.2 is given below:
(Figure 4.6).

3 4

Figure 4.6: CFG for program 4.2

Cyclomatic Complexity: This technique is used to find the number of independent

paths through a program. If CFG of a program is given, the Cyclomatic complexity
V(G) can be computed as: V(G) = E – N + 2, where N is the number of nodes of the
CFG and E is the number of edges in the CFG. For the example 4, the Cyclomatic
Complexity = 6 – 5 + 2 = 3.
The following are the properties of Cyclomatic complexity:

• V(G) is the maximum number of independent paths in graph G

• Inserting and deleting functional statements to G does not affect V(G)
• G has only one path if and only if V(G) = 1.
Mutation Testing
Mutation Testing is a powerful method for finding errors in software programs. In this
technique, multiple copies of programs are made, and each copy is altered; this altered
copy is called a mutant. Mutants are executed with test data to determine whether the
test data are capable of detecting the change between the original program and the
mutated program. The mutant that is detected by a test case is termed “killed” and the
goal of the mutation procedure is to find a set of test cases that are able to kill groups
of mutant programs. Mutants are produced by applying mutant operators. An operator
is essentially a grammatical rule that changes a single expression to another
expression. It is essential that all mutants must be killed by the test cases or shown to
be equivalent to the original expression. If we run a mutated program, there are two
possibilities:

1. The results of the program were affected by the code change and the test suite
detects it. We assumed that the test suite is perfect, which means that it must
detect the change. If this happens, the mutant is called a killed mutant.

2. The results of the program are not changed and the test suite does not detect the
mutation. The mutant is called an equivalent mutant.

If we take the ratio of killed mutants to all the mutants that were created, we get a
number that is smaller than 1. This number gives an indication of the sensitivity of
program to the changes in code. In real life, we may not have a perfect program and
we may not have a perfect test suite. Hence, we can have one more scenario:
3. The results of the program are different, but the test suite does not detect it
because it does not have the right test case.

62
Consider the following program 4.3: Software Testing

main(argc, argv) /* line 1 */

int argc; /* line 2 */
char *argv[]; /* line 3 */
{ /* line 4 */
int c=0; /* line 5 */
/* line 6 */
if(atoi(argv[1]) < 3){ /* line 7 */
printf("Got less than 3\n"); /* line 8 */
if(atoi(argv[2]) > 5) /* line 9 */
c = 2; /* line 10 */
} /* line 11 */
else /* line 12 */
printf("Got more than 3\n"); /* line 13 */
exit(0); /* line 14 */
} /* line 15 */

Program 4.3: A program

The program reads its arguments and prints messages accordingly.
Now let us assume that we have the following test suite that tests the program:
Test case 1:
Input: 2 4
Output: Got less than 3
Test case 2:
Input: 4 4
Output: Got more than 3
Test case 3:
Input: 4 6
Output: Got more than 3
Test case 4:
Input: 2 6
Output: Got less than 3
Test case 5:
Input: 4
Output: Got more than 3

Now, let’s mutate the program. We can start with the following simple changes:

Mutant 1: change line 9 to the form

if(atoi(argv[2]) <= 5)

Mutant 2: change line 7 to the form

if(atoi(argv[1]) >= 3)

Mutant 3: change line 5 to the form

int c=3;
If we take the ratio of all the killed mutants to all the mutants generated, we get a
number smaller than 1 that also contains information about accuracy of the test suite.
In practice, there is no way to separate the effect that is related to test suite inaccuracy
and that which is related to equivalent mutants. In the absence of other possibilities,
one can accept the ratio of killed mutants to all the mutants as the measure of the test
suite accuracy. The manner by which a test suite is evaluated via mutation testing is
as follows: For a specific test suite and a specific set of mutants, there will be three
types of mutants in the code (i) killed or dead (ii) live (iii) equivalent. The score
(evaluation of test suite) associated with a test suite T and mutants M is simply
computed as follows:
# killed Mutants
× 100

63
An Overview of # total mutants - # equivalent mutants
Software Engineering
) Check Your Progress 1
1) What is the use of Cyclomatic complexity in software development?
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………

4.3 TESTING ACTIVITIES

Although testing varies between organisations, there is a cycle to testing:
Requirements Analysis: Testing should begin in the requirements phase of the
software devlopment life cycle (SDLC).
Design Analysis: During the design phase, testers work with developers in
determining what aspects of a design are testable and under what parameters should
the testers work.
Test Planning: Test Strategy, Test Plan(s).
Test Development: Test Procedures, Test Scenarios, Test Cases, Test Scripts to use in
testing software.
Test Execution: Testers execute the software based on the plans and tests and report
any errors found to the development team.
Test Reporting: Once testing is completed, testers generate metrics and make final
reports on their test effort and whether or not the software tested is ready for release.
Retesting the Defects: Defects are once again tested to find whether they got
eliminated or not.
Levels of Testing:
Mainly, Software goes through three levels of testing:
• Unit testing
• Integration testing
• System testing.
Unit Testing
Unit testing is a procedure used to verify that a particular segment of source code is
working properly. The idea about unit tests is to write test cases for all functions or
methods. Ideally, each test case is separate from the others. This type of testing is
mostly done by developers and not by end users.
The goal of unit testing is to isolate each part of the program and show that the
individual parts are correct. Unit testing provides a strict, written contract that the
piece of code must satisfy. Unit testing will not catch every error in the program. By
definition, it only tests the functionality of the units themselves. Therefore, it will not
catch integration errors, perfomance problems and any other system-wide issues. A
unit test can only show the presence of errors; it cannot show the absence of errors.
Integration Testing
Integration testing is the phase of software testing in which individual software
modules are combined and tested as a group. It follows unit testing and precedes
system testing. Integration testing takes as its input, modules that have been checked
out by unit testing, groups them in larger aggregates, applies tests defined in an
integration test plan to those aggregates, and delivers as its output, the integrated
system ready for system testing.The purpose of Integration testing is to verify
functional, performance and reliability requirements placed on major design items.
64
System Testing Software Testing

System testing is conducted on a complete, integrated system to evaluate the system's

compliance with its specified requirements. As a rule, system testing takes, as its
input, all of the “integrated” software components that have successfully passed
integration testing and also the software system itself integrated with any applicable
hardware system(s). In system testing, the entire system can be tested as a whole
against the software requirements specification (SRS). There are rules that describe
the functionality that the vendor (developer) and a customer have agreed upon.
System testing tends to be more of an investigatory testing phase, where the focus is
to have a destructive attitude and test not only the design, but also the behavior and
even the believed expectations of the customer. System testing is intended to test up to
and beyond the bounds defined in the software requirements specifications.
Acceptance tests are conducted in case the software developed was a custom software
and not product based. These tests are conducted by customer to check whether the
software meets all requirements or not. These tests may range from a few weeks to
several months.

4.4 DEBUGGING
Debugging occurs as a consequence of successful testing. Debugging refers to the
process of identifying the cause for defective behavior of a system and addressing that
problem. In less complex terms - fixing a bug. When a test case uncovers an error,
debugging is the process that results in the removal of the error. The debugging
process begins with the execution of a test case. The debugging process attempts to
match symptoms with cause, thereby leading to error correction. The following are
two alternative outcomes of the debugging:

1. The cause will be found and necessary action such as correction or removal will
be taken.
2. The cause will not be found.
Characteristics of bugs
1. The symptom and the cause may be geographically remote. That is, the
symptom may appear in one part of a program, while the cause may
actually be located at a site that is far removed. Highly coupled program
structures exacerbate this situation.
2. The symptom may disappear (temporarily) when another error is corrected.
3. The symptom may actually be caused by non errors (e.g., round-off
inaccuracies).
4. The symptom may be caused by human error that is not easily traced.
5. The symptom may be a result of timing problems, rather than processing
problems.
6. It may be difficult to accurately reproduce input conditions (e.g., a real-time
application in which input ordering is indeterminate).
7. The symptom may be intermittent. This is particularly common in embedded
systems that couple hardware and software inextricably.
8. The symptom may be due to causes that are distributed across a number of
tasks running on different processors.
Life Cycle of a Debugging Task
The following are various steps involved in debugging:

65
An Overview of a) Defect Identification/Confirmation
Software Engineering
• A problem is identified in a system and a defect report created
• Defect assigned to a software engineer
• The engineer analyzes the defect report, performing the following actions:
¾ What is the expected/desired behaviour of the system?
¾ What is the actual behaviour?
¾ Is this really a defect in the system?
¾ Can the defect be reproduced? (While many times, confirming a defect is
straight forward. There will be defects that often exhibit quantum
behaviour.)
b) Defect Analysis
Assuming that the software engineer concludes that the defect is genuine, the focus
shifts to understanding the root cause of the problem. This is often the most
challenging step in any debugging task, particularly when the software engineer is
debugging complex software.
Many engineers debug by starting a debugging tool, generally a debugger and try to
understand the root cause of the problem by following the execution of the program
step-by-step. This approach may eventually yield success. However, in many
situations, it takes too much time, and in some cases is not feasible, due to the
complex nature of the program(s).
c) Defect Resolution
Once the root cause of a problem is identified, the defect can then be resolved by
making an appropriate change to the system, which fixes the root cause.
Debugging Approaches
Three categories for debugging approaches are:
• Brute force
• Backtracking
• Cause elimination.

Brute force is probably the most popular despite being the least successful. We apply
brute force debugging methods when all else fails. Using a “let the computer find the
error” technique, memory dumps are taken, run-time traces are invoked, and the
program is loaded with WRITE statements. Backtracking is a common debugging
method that can be used successfully in small programs. Beginning at the site where a
symptom has been uncovered, the source code is traced backwards till the error is
found. In Cause elimination, a list of possible causes of an error are identified and
tests are conducted until each one is eliminated.

) Check Your Progress 2

1) What are the different levels of testing and their goals? For each level
specify which of the testing approaches are most suitable.
……………………………………………………………………………..
……………………………………………………………………………..
2) Mention the steps involved in the process of debugging.
……………………………………………………………………………………
………....................................................................................................................

4.5 TESTING TOOLS

66
 Software Testing
The following are different categories of tools that can be used for testing:
• Data Acquisition: Tools that acquire data to be used during testing.
• Static Measurement: Tools that analyse source code without executing test
cases.
• Dynamic Measurement: Tools that analyse source code during execution.
• Simulation: Tools that simulate functions of hardware or other externals.
• Test Management: Tools that assist in planning, development and control of
testing.
• Cross-Functional tools: Tools that cross the bounds of preceding categories.
The following are some of the examples of commercial software testing tools:
Rational Test Real Time Unit Testing
• Kind of Tool
Rational Test RealTime's Unit Testing feature automates C, C++ software
component testing.
• Organisation
IBM Rational Software
• Software Description
Rational Test RealTime Unit Testing performs black-box/functional testing, i.e.,
verifies that all units behave according to their specifications without regard to how
that functionality is implemented. The Unit Testing feature has the flexibility to
naturally fit any development process by matching and automating developers' and
testers' work patterns, allowing them to focus on value-added tasks. Rational Test
RealTime is integrated with native development environments (Unix and Windows)
as well as with a large variety of cross-development environments.
• Platforms
Rational Test RealTime is available for most development and target systems
including Windows and Unix.
AQtest
• Kind of Tool
Automated support for functional, unit, and regression testing
• Organisation
AutomatedQA Corp.
• Software Description
AQtest automates and manages functional tests, unit tests and regression tests, for
applications written with VC++, VB, Delphi, C++Builder, Java or VS.NET. It also
supports white-box testing, down to private properties or methods. External tests can
be recorded or written in three scripting languages (VBScript, JScript, DelphiScript).
Using AQtest as an OLE server, unit-test drivers can also run it directly from
application code. AQtest automatically integrates AQtime when it is on the machine.
Entirely COM-based, AQtest is easily extended through plug-ins using the complete
IDL libraries supplied. Plug-ins currently support Win32 API calls, direct ADO
access, direct BDE access, etc.
• Platforms
Windows 95, 98, NT, or 2000.

67
An Overview of csUnit
Software Engineering
• Kind of Tool
“Complete Solution Unit Testing” for Microsoft .NET (freeware)
• Organisation
csUnit.org
• Software Description
csUnit is a unit testing framework for the Microsoft .NET Framework. It
targets test driven development using .NET languages such as C#, Visual
Basic .NET, and managed C++.
• Platforms
Microsoft Windows
Sahi
http://sahi.sourceforge.net/
Software Description
Sahi is an automation and testing tool for web applications, with the facility to record
and playback scripts. Developed in Java and JavaScript, it uses simple JavaScript to
execute events on the browser. Features include in-browser controls, text based
scripts, Ant support for playback of suites of tests, and multi-threaded playback. It
supports HTTP and HTTPS. Sahi runs as a proxy server and the browser needs to use
the Sahi server as its proxy. Sahi then injects JavaScript so that it can access elements
in the webpage. This makes the tool independant of the website/ web application.
• Platforms
OS independent. Needs at least JDK1.4

4.6 SUMMARY
The importance of software testing and its impact on software is explained in this unit.
Software testing is a fundamental component of software development life cycle and
represents a review of specification, design and coding. The objective of testing is to
have the highest likelihood of finding most of the errors within a minimum amount of
time and minimal effort. A large number of test case design methods have been
developed that offer a systematic approach to testing to the developer.

Knowing the specified functions that the product has been designed to perform, tests
can be performed that show that each function is fully operational. A strategy for
software testing may be to move upwards along the spiral. Unit testing happens at the
vortex of the spiral and concentrates on each unit of the software as implemented by
the source code. Testing happens upwards along the spiral to integration testing,
where the focus is on design and production of the software architecture. Finally, we
perform system testing, where software and other system elements are tested together.
Debugging is not testing, but always happens as a response of testing. The debugging
process will have one of two outcomes:
1) The cause will be found, then corrected or removed, or
2) The cause will not be found. Regardless of the approach that is used, debugging
has one main aim: to determine and correct errors. In general, three kinds of
debugging approaches have been put forward: Brute force, Backtracking and
Cause elimination.

68
 Software Testing
4.7 SOLUTIONS / ANSWERS
Check Your Progress 1
1) Cyclomatic Complexity is asoftware metric that provides a quantitative
measure of the logical complexity of a program. When it is used in the context
of the basis path testing method, the value computed for Cyclomatic complexity
defines the number of independent paths in the basis set of a program. It also
provides an upper bound for the number of tests that must be conducted to
ensure that all statements have been executed at least once.

Check Your Progress 2

1) The basic levels of testing are: unit testing, integration testing, system
testing and acceptance testing.

Clients need Acceptance Testing

Requirements System Testing

Design Integration Testing

Code Unit Testing

Figure 4.7: Testing levels

For unit testing, structural testing approach is best suited because the focus of testing
is on testing the code. In fact, structural testing is not very suitable for large programs.
It is used mostly at the unit testing level. The next level of testing is integration testing
and the goal is to test interfaces between modules. With integration testing, we move
slowly away from structural testing and towards functional testing. This testing
activity can be considered for testing the design. The next levels are system and
acceptance testing by which the entire software system is tested. These testing levels
focus on the external behavior of the system. The internal logic of the program is not
emphasized. Hence, mostly functional testing is performed at these levels.
2) The various steps involved in debugging are:
• Defect Identification/Confirmation
• Defect Analysis
• Defect Resolution

4.8 FURTHER READINGS

1) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson

Education.
2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman;
McGraw-Hill International Edition.

69
An Overview of 3) An Integrated approach to Software Engineering, Pankaj Jalote; Narcosis
Software Engineering Publishing House.
Reference websites
http://www.rspa.com
http://www.ieee.org
http://standards.ieee.org
http://www.ibm.com
http://www.opensourcetesting.org

70
 Software Project
UNIT 1 SOFTWARE PROJECT PLANNING Planning

Structure Page Nos.

1.0 Introduction 5
1.1 Objectives 5
1.2 Different Types of Project Metrics 5
1.3 Software Project Estimation 9
1.3.1 Estimating the Size
1.3.2 Estimating Effort
1.3.3 Estimating Schedule
1.3.4 Estimating Cost
1.4 Models for Estimation 13
1.4.1 COCOMO Model
1.4.2 Putnam’s Model
1.4.3 Statistical Model
1.4.4 Function Points
1.5 Automated Tools for Estimation 15
1.6 Summary 17
1.7 Solutions/Answers 17
1.8 Further Readings 17

1.0 INTRODUCTION

Historically, software projects have dubious distinction of overshooting project

schedule and cost. Estimating duration and cost continues to be a weak link in
software project management. The aim of this unit is to give an overview of different
project planning techniques and tools used by modern day software project managers.

It is the responsibility of the project manager to make as far as possible accurate

estimations of effort and cost. This is particularly what is desired by the management
of an organisation in a competitive world. This is specially true of projects subject to
competition in the market where bidding too high compared with competitors would
result in losing the business and a bidding too low could result in financial loss to the
organisation. This makes software project estimation crucial for project managers.

1.1 OBJECTIVES

After going through this unit, you should be able to:

• understand different software estimation techniques;

• understand types of metrics used for software project estimation;
• learn about models used for software estimation, and
• learn about different automated tools used for estimation.

1.2 DIFFERENT TYPES OF PROJECT METRICS

It is said that if you cannot measure, then, it is not engineering. Effective

management of software development process requires effective measurement of
software development process. Often, from the input given by project leaders on the
estimation of a software project, the management decides whether to proceed with
the project or not.
5
Software Project The process of software estimation can be defined as the set of techniques and
Management
procedures that an organisation uses to arrive at an estimate. An important aspect of
software projects is to know the cost, time, effort, size etc.

Need for Project metrics : Historically, the process of software development has been
witnessing inaccurate estimations of schedule and cost, overshooting delivery target
and productivity of software engineers in not commensurate with the growth of
demand. Software development projects are quite complex and there was no scientific
method of measuring the software process. Thus effective measurement of the process
was virtually absent. The following phrase is aptly describing the need for
measurement:

If you can not measure it, then, you can not improve it.

This is why measurement is very important to software projects. Without the process
of measurement, software engineering cannot be called engineering in the true sense.

Definition of metrics : Metrics deal with measurement of the software process and the
software product. Metrics quantify the characteristics of a process or a product.
Merics are often used to estimate project cost and project schedule.

Examples of metrics : Lines of code(LOC), pages of documentation, number of man-

months, number of test cases, number of input forms.

Types of Project metrics

Metrics can be broadly divided into two categories namely, product metrics and
process metrics.

Product metrics provides a measure of a software product during the process of

development which can be in terms of lines of code (either source code or object
code), pages of documentation etc.

Process metrics is a measure of the software development process such as time,

effort etc.

Another way of classification of metrics are primitive metrics and derived metrics.

Primitive metrics are directly observable quantities like lines of code (LOC), number
of man-hours etc.

Derived metrics are derived from one or more of primitive metrics like lines of code
per man-hour, errors per thousand lines of code.

Now, let us briefly discuss different types of product metrics and process metrics.

Product metrics

Lines of Code(LOC) : LOC metric is possibly the most extensively used for
measurement of size of a program. The reason is that LOC can be precisely defined.
LOC may include executable source code and non-executable program code like
comments etc.

Looking at the following table, we can know the size of a module.

Module Effort in man-months LOC

Module 1 3 24,000
Module 2 4 25,000
6
Looking at the data above we have a direct measure of the size of the module in terms Software Project
of LOC. We can derive a productivity metrics from the above primitive metrics Planning
i.e., LOC.

Productivity of a person = LOC / man-month

Quality = No. of defects / LOC

It is evident that the productivity of the developer engaged in Module 1 is more than
the productivity of the developer engaged in Module 2. It is important to note here
how derived metrics are very handy to project managers to measure various aspects of
the projects.

Although, LOC provides a direct measure of program size, at the same time, these
metrics are not universally accepted by project managers. Looking at the data in the
table below, it can be easily observed that LOC is not an absolute measure of
program size and largely depends on the computer language and tools used for
development activity.

Consider the following table:

Module Effort in LOC in COBOL LOC in LOC in 4 GL

man- Assembly
months
Module- 1 3 24,000 800,000 400
Module- 2 4 25,000 100,000 500

The LOC of same module varies with the programming language used. Hence, just
LOC cannot be an indicator of program size. The data given in the above table is only
assumed and does not correspond to any module(s).

There are other attributes of software which are not directly reflected in Lines of Code
(LOC), as the complexity of the program is not taken into account in LOC and it
penalises well designed shorter program. Another disadvantage of LOC is that the
project manager is supposed to estimate LOC before the analysis and design is
complete.

Function point : Function point metrics instead of LOC measures the functionality of
the program. Function point analysis was first developed by Allan J. Albrecht in the
1970s. It was one of the initiatives taken to overcome the problems associated with
LOC.

In a Function point analysis, the following features are considered:

• External inputs : A process by which data crosses the boundary of the system.
Data may be used to update one or more logical files. It may be noted that data
here means either business or control information.

• External outputs : A process by which data crosses the boundary of the system
to outside of the system. It can be a user report or a system log report.

• External user inquires : A count of the process in which both input and output
results in data retrieval from the system. These are basically system inquiry
processes.

• Internal logical files : A group of logically related data files that resides
entirely within the boundary of the application software and is maintained
through external input as described above.

7
Software Project • External interface files : A group of logically related data files that are used
Management
by the system for reference purposes only. These data files remain completely
outside the application boundary and are maintained by external applications.

As we see, function points, unlike LOC, measure a system from a functional

perspective independent of technology, computer language and development method.
The number of function points of a system will remain the same irrespective of the
language and technology used.

For transactions like external input, external output and user inquiry, the ranking of
high, low and medium will be based on number of file updated for external inputs or
number of files referenced for external input and external inquiries. The complexity
will also depend on the number of data elements.

Consider the following classification for external inquiry:

No. of Data Number of file references

elements 0 to 2 3 to 4 5 and above
1 to 5 Low Low Low
6 to 10 Low Medium Medium
10 to 20 Medium Medium High
More than 20 Medium High High

Also, External Inquiry, External Input and External output based on complexity can
be assigned numerical values like rating.

Component type Values

Low Medium High
External Output 4 6 8
External Input 2 4 6
External Inquiry 3 5 7

Similarly, external logical files and external interface files are assigned numerical
values depending on element type and number of data elements.

Component type Values

Low Medium High
External Logical files 6 8 10
External Interface 5 7 9

Organisations may develop their own strategy to assign values to various function
points. Once the number of function points have been identified and their significance
has been arrived at, the total function point can be calculated as follows.

Type of Complexity of component

Component Low Medium High Total
Number of X4= X6= X8=
External Output
Number of X2= X4= X6=
External Input
Number of X3 = X5= X7=
External Inquiry
Number of X6= X8= X 10 =
Logical files
Number of X5= X7= X9=
Interface file
Total of function point

8
Total of function points is calculated based on the above table. Once, total of function Software Project
points is calculated, other derived metrics can be calculated as follows: Planning

Productivity of Person = Total of Function point / man-month

Quality = No. of defects / Total of Function points.

Benefits of Using Function Points

• Function points can be used to estimate the size of a software application correctly
irrespective of technology, language and development methodology.
• User understands the basis on which the size of software is calculated as these are
derived directly from user required functionalities.
• Function points can be used to track and monitor projects.
• Function points can be calculated at various stages of software development
process and can be compared.

Other types of metrics used for various purposes are quality metrics which
include the following:

• Defect metrics : It measures the number of defects in a software product. This

may include the number of design changes required, number of errors detected in
the test, etc.

• Reliability metrics : These metrics measure mean time to failure. This can be
done by collecting data over a period of time.

) Check Your Progress 1

1) Lines of Code (LOC) is a product metric. True False
2) _______ are examples of process metrics.

1.3 SOFTWARE PROJECT ESTIMATION

Software project estimation is the process of estimating various resources required for
the completion of a project. Effective software project estimation is an important
activity in any software development project. Underestimating software project and
under staffing it often leads to low quality deliverables, and the project misses the
target deadline leading to customer dissatisfaction and loss of credibility to the
company. On the other hand, overstaffing a project without proper control will
increase the cost of the project and reduce the competitiveness of the company.

Software project estimation mainly encompasses the following steps:

• Estimating the size of project. There are many procedures available for estimating
the size of a project which are based on quantitative approaches like estimating
Lines of Code or estimating the functionality requirements of the project called
Function point.

• Estimating efforts based on man-month or man-hour. Man-month is an estimate of

personal resources required for the project.

• Estimating schedule in calendar days/month/year based on total man-month

required and manpower allocated to the project
Duration in calendar month = Total man-months / Total manpower allocated.

9
Software Project • Estimating total cost of the project depending on the above and other
Management
resources.

In a commercial and competitive environment, Software project estimation is crucial

for managerial decision making. The following Table give the relationship between
various management functions and software metrics/indicators. Project estimation and
tracking help to plan and predict future projects and provide baseline support for
project management and supports decision making.

Consider the following table:

Activity Tasks involved

Planning Cost estimation, planning for training of manpower,
project scheduling and budgeting the project
Controlling Size metrics and schedule metrics help the manager to
keep control of the project during execution
Monitoring/improving Metrics are used to monitor progress of the project and
wherever possible sufficient resources are allocated to
improve.

Figure 1.1 depicts the software project estimation.

User requirements

Schedule
Constraints Software Project
estimation Effort
Cost

Organisational
policies, Standards

Figure 1.1: Software project estimation

1.3.1 Estimating the size

Estimating the size of the software to be developed is the very first step to make an
effective estimation of the project. Customer’s requirements and system specification
forms a baseline for estimating the size of a software. At a later stage of the project,
system design document can provide additional details for estimating the overall size
of a software.

• The ways to estimate project size can be through past data from an earlier
developed system. This is called estimation by analogy.
• The other way of estimation is through product feature/functionality. The system
is divided into several subsystems depending on functionality, and size of each
subsystem is calculated.

1.3.2 Estimating effort

Once the size of software is estimated, the next step is to estimate the effort based on
the size. The estimation of effort can be made from the organisational specifics of
software development life cycle. The development of any application software system
is more than just coding of the system. Depending on deliverable requirements, the
estimation of effort for project will vary. Efforts are estimated in number of man-
months.
10
• The best way to estimate effort is based on the organisation’s own historical data Software Project
of development process. Organizations follow similar development life cycle for Planning
developing various applications.

• If the project is of a different nature which requires the organisation to adopt a

different strategy for development then different models based on algorithmic
approach can be devised to estimate effort.

1.3.3 Estimating Schedule

The next step in estimation process is estimating the project schedule from the effort
estimated. The schedule for a project will generally depend on human resources
involved in a process. Efforts in man-months are translated to calendar months.
Schedule estimation in calendar-month can be calculated using the following model
[McConnell]:
Schedule in calendar months = 3.0 * (man-months) 1/3
The parameter 3.0 is variable, used depending on the situation which works best for
the organisation.

1.3.4 Estimating Cost

Cost estimation is the next step for projects. The cost of a project is derived not only
from the estimates of effort and size but from other parameters such as hardware,
travel expenses, telecommunication costs, training cost etc. should also be taken into
account.
Figure 1.2 depicts the cost estimation process.
Effort

Hardware cost
Cost estimation
Travel expenses Project cost
process
Training cost

Communication cost
and other cost
factors
Figure 1.2 : Cost estimation process

Figure 1.3 depicts project estimation process.

User requirements

Data from past Estimate size Resources

projects

Estimate effort Estimate

schedule

Estimate Cost

Figure 1.3: Project estimation process

11
Software Project Now, once the estimation is complete, we may be interested to know how accurate the
Management
estimates are to reality. The answer to this is “we do not know until the project is
complete”. There is always some uncertainty associated with all estimation
techniques. The accuracy of project estimation will depend on the following:

• Accuracy of historical data used to project the estimation

• Accuracy of input data to various estimates
• Maturity of organisation’s software development process.

The following are some of the reasons which make the task of cost estimation
difficult:

• Software cost estimation requires a significant amount of effort. Sufficient time is

not allocated for planning.
• Software cost estimation is often done hurriedly, without an appreciation for the
actual effort required and is far from real issues.
• Lack of experience for developing estimates, especially for large projects.
• An estimator uses the extrapolation technique to estimate, ignoring the non-linear
aspects of software development process

The following are some of the reasons for poor and inaccurate estimation:

• Requirements are imprecise. Also, requirements change frequently.

• The project is new and is different from past projects handled.
• Non-availability of enough information about past projects.
• Estimates are forced to be based on available resources.

Cost and time tradeoffs

If we elongate the project, we can reduce overall cost. Usually, long project durations
are not liked by customers and managements. There is always shortest possible
duration for a project, but it comes at a cost.

The following are some of the problems with estimates:

• Estimating size is often skipped and a schedule is estimated which is of more

relevance to the management.
• Estimating size is perhaps the most difficult step which has a bearing on all other
estimates.
• Let us not forget that even good estimates are only projections and subject to
various risks.
• Organisations often give less importance to collection and analysis of historical
data of past development projects. Historical data is the best input to estimate a
new project.
• Project managers often underestimate the schedule because management and
customers often hesitate to accept a prudent realistic schedule.

Project estimation guidelines

• Preserve and document data pertaining to organisation’s past projects.

• Allow sufficient time for project estimation especially for bigger projects.
• Prepare realistic developer-based estimate. Associate people who will work on the
project to reach at a realistic and more accurate estimate.
• Use software estimation tools.
• Re-estimate the project during the life cycle of development process.
• Analyse past mistakes in the estimation of projects.

12
) Check Your Progress 2 Software Project
Planning

1) What is the first step in software project estimation?

……………………………………………………………………………
2) What are the major inputs for software project estimation?
……………………………………………………………………………

1.4 MODELS FOR ESTIMATION

Estimation based on models allows us to estimate projects ignoring less significant

parameters and concentrating on crucial parameters that drive the project estimate.
Models are analytic and empirical in nature. The estimation models are based on the
following relationship:

E = f (vi)

E = different project estimates like effort, cost, schedule etc.

vi = directly observable parameter like LOC, function points

1.4.1 COCOMO Model

COCOMO stands for Constructive Cost Model. It was introduced by Barry Boehm.
It is perhaps the best known and most thoroughly documented of all software cost
estimation models. It provides the following three level of models:

• Basic COCOMO : A single-value model that computes software development

cost as a function of estimate of LOC.

• Intermediate COCOMO : This model computes development cost and effort as

a function of program size (LOC) and a set of cost drivers.

• Detailed COCOMO : This model computes development effort and cost which
incorporates all characteristics of intermediate level with assessment of cost
implication on each step of development (analysis, design, testing etc.).

This model may be applied to three classes of software projects as given below:

• Organic : Small size project. A simple software project where the development
team has good experience of the application

• Semi-detached : An intermediate size project and project is based on rigid and

semi-rigid requirements.

• Embedded : The project developed under hardware, software and operational

constraints. Examples are embedded software, flight control software.

In the COCOMO model, the development effort equation assumes the following form:

E = aSb m
where a and b are constraints that are determined for each model.
E = Effort
S = Value of source in LOC
m = multiplier that is determined from a set of 15 cost driver’s attributes.
13
Software Project The following are few examples of the above cost drivers:
Management

• Size of the application database

• Complexity of the project
• Reliability requirements for the software
• Performance constraints in run-time
• Capability of software engineer
• Schedule constraints.

Barry Boehm suggested that a detailed model would provide a cost estimate to the
accuracy of ± 20 % of actual value

1.4.2 Putnam’s model

L. H. Putnam developed a dynamic multivariate model of the software development

process based on the assumption that distribution of effort over the life of software
development is described by the Rayleigh-Norden curve.

P = Kt exp(t2/2T2) / T2

P = No. of persons on the project at time ‘t’

K = The area under Rayleigh curve which is equal to total life cycle effort
T = Development time

The Rayleigh-Norden curve is used to derive an equation that relates lines of code
delivered to other parameters like development time and effort at any time during the
project.

S = CkK1/3T4/3

S = Number of delivered lines of source code (LOC)

Ck = State-of-technology constraints
K = The life cycle effort in man-years
T = Development time.

1.4.3 Statistical Model

From the data of a number of completed software projects, C.E. Walston and
C.P. Felix developed a simple empirical model of software development effort with
respect to number of lines of code. In this model, LOC is assumed to be directly
related to development effort as given below:

E = a Lb

Where L = Number of Lines of Code (LOC)

E = total effort required

a and b are parameters obtained from regression analysis of data. The final equation is
of the following form:

E = 5.2 L0.91

The productivity of programming effort can be calculated as

P = L/E

Where P = Productivity Index

14
1.4.4 Function Points Software Project
Planning
It may be noted that COCOMO, Putnam and statistical models are based on LOC. A
number of estimation models are based on function points instead of LOC. However,
there is very little published information on estimation models based on function
points.

1.5 AUTOMATED TOOLS FOR ESTIMATION

After looking at the above models for software project estimation, we have reason to
think of software that implements these models. This is what exactly the automated
estimation tools do. These estimation tools, which estimate cost and effort, allow the
project managers to perform “What if analysis”. Estimation tools may only support
size estimation or conversion of size to effort and schedule to cost.

There are more than dozens of estimation tools available. But, all of them have the
following common characteristics:

• Quantitative estimates of project size (e.g., LOC).

• Estimates such as project schedule, cost.
• Most of them use different models for estimation.

Figure 1.4 depicts a typical structure of estimation tools.

Reports
Size estimation Project
tool estimation Cost
Requirements Schedule
tools
Effort

Other cost drivers

and constraints

Figure 1.4: Typical structure of estimation tools

No estimation tool is the solution to all estimation problems. One must understand
that the tools are just to help the estimation process.

Problems with Models

Most models require an estimate of software product size. However, software size is
difficult to predict early in the development lifecycle. Many models use LOC for
sizing, which is not measurable during requirements analysis or project planning.
Although, function points and object points can be used earlier in the lifecycle, these
measures are extremely subjective.

Size estimates can also be very inaccurate. Methods of estimation and data collection
must be consistent to ensure an accurate prediction of product size. Unless the size
metrics used in the model are the same as those used in practice, the model will not
yield accurate results (Fenton, 1997).

15
Software Project
Management
The following Table gives some estimation tools:

Automated Estimation Tools

Tool Tool vendor site Functionality/Remark

EstimatorPal http://www.effortestimator.com/ EstimatorPal© is a software
tool that assists software
developers estimate the
effort required to be spent
on various activities.

This tool facilitates use of

the following Estimation
techniques –
Effort estimation tools
which supports Function
Point Analysis Technique.,
Objects Points Technique,
Use Case Points Technique
and Task-Based Estimation
Technique
Estimate Easy Use Duvessa Software Effort estimation tool based
Case http://www.duvessa.com/ on use cases
USC COCOMO II USC Center for Software Engineering Based on COCOMO
http://sunset.usc.edu/research/COCOMOII/index.html
ESTIMACS Computer Associates International Inc. Provides estimates of the
http://www.cai.com/products/estimacs.htm effort, duration, cost and
personnel requirements for
maintenance and new
application development
projects.
Checkpoint Software Productivity Research Inc. Guides the user through the
http://www.spr.com/ development of a software
project estimate and plan.
Function Point Software Productivity Research Inc. Automated software
Workbench http://www.spr.com/ estimation tools,
implementing function point
sizing techniques, linking
project estimation to project
management initiatives, and
collecting historical project
data to improve future
estimation efforts
ESTIMATE Software Productivity Center Based on Putnam,
Professional http://www.spc.com COCOMO II
SEER-SEM Galorath Predicts, measures and
http://www.galorath.com/ analyzes resources, staffing,
schedules, risk and cost for
software projects
ePM.Ensemble InventX Support effort estimation,
http://www.inventx.com/ among other things.
CostXpert Marotz, Inc. Based on COCOMO
http://www.costxpert.com/

16
 Software Project
1.6 SUMMARY Planning

Estimation is an integral part of the software development process and should not be
taken lightly. A well planned and well estimated project is likely to be completed in
time. Incomplete and inaccurate documentation may pose serious hurdles to the
success of a software project during development and implementation. Software cost
estimation is an important part of the software development process. Metrics are
important tools to measure software product and process. Metrics are to be selected
carefully so that they provide a measure for the intended process/product. Models are
used to represent the relationship between effort and a primary cost factor such as
software product size. Cost drivers are used to adjust the preliminary estimate
provided by the primary cost factor. Models have been developed to predict software
cost based on empirical data available, but many suffer from some common problems.
The structure of most models is based on empirical results rather than theory. Models
are often complex and rely heavily on size estimation. Despite problems, models are
still important to the software development process. A model can be used most
effectively to supplement and corroborate other methods of estimation.

1.7 SOLUTIONS/ANSWERS

Check Your Progress 1

1. True
2. Time, Schedule

Check Your Progress 2

1. Estimating size of the Project

2. User requirements, and project constraints.

1.8 FURTHER READINGS

1) Software Engineering, Ian Sommerville; Sixth Edition, 2001, Pearson Education.

2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman; McGraw-

Hill International Edition.

Reference websites

http://www.rspa.com
http://www.ieee.org
http://www.ncst.ernet.in

17
Software Project
Management UNIT 2 RISK MANAGEMENT AND
PROJECT SCHEDULING
Structure Page Nos.

2.0 Introduction 18
2.1 Objectives 18
2.2 Identification of Software Risks 18
2.3 Monitoring of Risks 20
2.4 Management of Risks 20
2.4.1 Risk Management
2.4.2 Risk Avoidance
2.4.3 Risk Detection
2.5 Risk Control 22
2.6 Risk Recovery 23
2.7 Formulating a Task Set for the Project 24
2.8 Choosing the Tasks of Software Engineering 24
2.9 Scheduling Methods 25
2.10 The Software Project Plan 27
2.11 Summary 28
2.12 Solutions/Answers 28
2.13 Further Readings 30

2.0 INTRODUCTION

As human beings, we would like life to be free from dangers, difficulties and any risks
of any type. In case a risk arises, we would take proper measures to recover as soon as
possible. Similarly, in software engineering, risk management plays an important role
for successful deployment of the software product. Risk management involves
monitoring of risks, taking necessary actions in case risk arises by applying risk
recovery methods.

2.1 OBJECTIVES

After going through this unit, you should be able to:

• know the meaning of risk;

• identify risks; and
• manage the risks

2.2 IDENTIFICATION OF SOFTWARE RISKS

A risk may be defined as a potential problem. It may or may not occur. But, it should
always be assumed that it may occur and necessary steps are to be taken.
Risks can arise from various factors like improper technical knowledge or lack of
communication between team members, lack of knowledge about software products,
market status, hardware resources, competing software companies, etc.

Basis for Different Types of Software risks

• Skills or Knowledge: The persons involved in activities of problem analysis,

design, coding and testing have to be fully aware of the activities and various
18
 techniques at each phase of the software development cycle. In case, they Risk Management and
have partial knowledge or lacks adequate skill, the products may face many Project Scheduling
risks at the current stage of development or at later stages.

• Interface modules: Complete software contains various modules and each

module sends and receives information to other modules and their concerned
data types have to match.

• Poor knowledge of tools: If the team or individual members have poor

knowledge of tools used in the software product, then the final product will
have many risks, since it is not thoroughly tested.

• Programming Skills: The code developed has to be efficient, thereby,

occupying less memory space and less CPU cycles to compute given task.
The software product should be able to implement various object oriented
techniques and be able to catch exceptions in case of errors. Various data
values have to be checked and in case of improper values, appropriate
messages have to be displayed. If this is not done, then it leads to risk, thereby
creating panic in the software computations.

• Management Issues : The management of the organisation should give

proper training to the project staff, arrange some recreation activities, give
bonus and promotions and interact with all members of the project and try to
solve their necessities at the best. It should take care that team members and
the project manager have healthy coordination, and in case there are some
differences they should solve or make minor shuffles.

• Updates in the hardware resources: The team should be aware of the latest
updates in the hardware resources, such as latest CPU (Intel P4, Motorola
series, etc.), peripherals, etc. In case the developer makes a product, and later
in the market, a new product is released, the product should support minimum
features. Otherwise, it is considered a risk, and may lead to the failure of the
project.

• Extra support: The software should be able to support a set of a few extra
features in the vicinity of the product to be developed.

• Customer Risks: Customer should have proper knowledge of the product

needed, and should not be in a hurry to get the work done. He should take
care that all the features are implemented and tested. He should take the help
of a few external personnel as needed to test the product and should arrange
for demonstrations with a set of technical and managerial persons from his
office.

• External Risks: The software should have backup in CD, tapes, etc., fully
encrypted with full licence facilities. The software can be stored at various
important locations to avoid any external calamities like floods, earthquakes,
etc. Encryption is maintained such that no external persons from the team can
tap the source code.

• Commercial Risks: The organisation should be aware of various competing

vendors in the market and various risks involved if their product is not
delivered on time. They should have statistics of projects and risks involved
from their previous experience and should have skilled personnel.

19
Software Project
Management 2.3 MONITORING OF RISKS

Various risks are identified and a risk monitor table with attributes like risk name,
module name, team members involved, lines of code, codes affecting this risk,
hardware resources, etc., is maintained. If the project is continued further to 2-3
weeks, and then further the risk table is also updated. It is seen whether there is a
ripple effect in the table, due to the continuity of old risks. Risk monitors can change
the ordering of risks to make the table easy for computation. Table 2.1 depicts a risk
table monitor. It depicts the risks that are being monitored.
Table 2.1: Risk table monitor

Sl. No. Risk Name Week 1 Week 2 Remarks

1. Module compute() Line 5, 8, 20 Line 5,25 Priority 3

2. More memory and Module f1(), Module f2() Priority 1

peripherals f5() affected affected
...... .......... .......... ............. ............

The above risk table monitor has a risk in module compute () where there is a risk in
line 5, 8 and 20 in week 1. In week 2, risks are present in lines 5 and 25. Risks are
reduced in week 2. The priority 3 is set. Similarly, in the second row, risk is due to
more memory and peripherals, affecting module f1 (), f5 () in week-1. After some
modifications in week 2, module f2 () is affected and the priority is set to 1.

) Check Your Progress 1

1) Define the term risk and how it is related to software engineering.
……………………………………………………………………………………
……………………………………………………………………………………
2) List at least two risks involved with the management of team members.
……………………………………………………………………………………
……………………………………………………………………………………
3) What are commercial risks?
……………………………………………………………………………………
……………………………………………………………………………………
4) What do you mean by monitoring of risks and describe risk table.
……………………………………………………………………………………
……………………………………………………………………………………
5) Mention any two ways to prioritise risks.
……………………………………………………………………………………
……………………………………………………………………………………

2.4 MANAGEMENT OF RISKS

Risk management plays an important role in ensuring that the software product is
error free. Firstly, risk management takes care that the risk is avoided, and if it not
avoidable, then the risk is detected, controlled and finally recovered.
The flow of risk management is as follows:
20
2.4.1 Risk Management Risk Management and
Project Scheduling
A priority is given to risk and the highest priority risk is handled first. Various factors
of the risk are who are the involved team members, what hardware and software items
are needed, where, when and why are resolved during risk management. The risk
manager does scheduling of risks. Risk management can be further categorised as
follows:
1. Risk Avoidance
a. Risk anticipation
b. Risk tools
2. Risk Detection
a. Risk analysis
b. Risk category
c. Risk prioritisation
3. Risk Control
a. Risk pending
b. Risk resolution
c. Risk not solvable
4. Risk Recovery
a. Full
b. Partial
c. Extra/alternate features

Figure 2.1 depicts a risk manager tool.

Start Risk
Manager

True Risk • Risk Anticipate

Avoidance • Risk tools

No • Risk Analysis
Risk Detection
• Risk Category
• Risk Prioritisation
Detect
• Risk Pending
Risk Control • Risk Resolution
• Risk Not Solvable

Risk Recovery • Full

• Partial
• Extra/alternate

End Risk
Manager

Figure 2.1 : Risk Manager Tool

21
Software Project From the Figure 2.1, it is clear that the first phase is to avoid risk by anticipating and
Management using tools from previous project history. In case there is no risk, risk manager halts.
In case there is risk, detection is done using various risk analysis techniques and
further prioritising risks. In the next phase, risk is controlled by pending risks,
resolving risks and in the worst case (if risk is not solved) lowering the priority.
Lastly, risk recovery is done fully, partially or an alternate solution is found.

2.4.2 Risk Avoidance

Risk Anticipation: Various risk anticipation rules are listed according to standards
from previous projects’ experience, and also as mentioned by the project manager.

Risk tools: Risk tools are used to test whether the software is risk free. The tools have
built-in data base of available risk areas and can be updated depending upon the type
of project.

2.4.3 Risk Detection

The risk detection algorithm detects a risk and it can be categorically stated as :

Risk Analysis: In this phase, the risk is analyzed with various hardware and software
parameters as probabilistic occurrence (pr), weight factor (wf) (hardware resources,
lines of code, persons), risk exposure (pr * wf).

Table 2.1 depicts a risk analysis table.

Table 2.1: Risk analysis table

Sl.No. Risk Name Probability of Weight factor Risk

occurrence (wf) exposure
(pr) (pr * wf)
1. Stack 5 15 75
overflow
2. No Password 7 20 140
forgot option
.... ....... ....... ...... .....

Maximum value of risk exposure indicates that the problem has to solved as soon as
possible and be given high priority. A risk analysis table is maintained as shown
above.

Risk Category: Risk identification can be from various factors like persons involved in
the team, management issues, customer specification and feedback, environment,
commercial, technology, etc. Once proper category is identified, priority is given
depending upon the urgency of the product.

Risk Prioritisation: Depending upon the entries of the risk analysis table, the
maximum risk exposure is given high priority and has to be solved first.

2.5 RISK CONTROL

Once the prioritisation is done, the next step is to control various risks as follows:

• Risk Pending: According to the priority, low priority risks are pushed at the end
of the queue with a view of various resources (hardware, man power, software)
and in case it takes more time their priority is made higher.
22
• Risk Resolution: Risk manager makes a strong resolve how to solve the risk. Risk Management and
Project Scheduling
• Risk elimination: This action leads to serious error in software.

• Risk transfer: If the risk is transferred to some part of the module, then risk
analysis table entries get modified. Thereby, again risk manager will control high
priority risk.

• Disclosures: Announce the risk of less priority to the customer or display

message box as a warning. And thereby the risk is left out to the user, such that he
should take proper steps during data entry, etc.

• Risk not solvable: If a risk takes more time and more resources, then it is dealt in
its totality in the business aspect of the organisation and thereby it is notified to
the customer, and the team member proposes an alternate solution. There is a
slight variation in the customer specification after consultation.

2.6 RISK RECOVERY

Full : The risk analysis table is scanned and if the risk is fully solved, then
corresponding entry is deleted from the table.

Partial : The risk analysis table is scanned and due to partially solved risks, the
entries in the table are updated and thereby priorities are also updated.

Extra/alternate features : Sometimes it is difficult to remove some risks, and in that

case, we can add a few extra features, which solves the problem. Therefore, a bit of
coding is done to get away from the risk. This is later documented or notified to the
customer.

) Check Your Progress 2

1) Define the term risk management
……………………………………………………………………………………
……………………………………………………………………………………
2) What are various phases of risk manager?
……………………………………………………………………………………
……………………………………………………………………………………
3) What are the attributes mentioned in risk analysis table?
……………………………………………………………………………………
……………………………………………………………………………………
4) What is meant by risk resolution?
……………………………………………………………………………………
……………………………………………………………………………………
5) Why do we add extra features to recover from risks?
……………………………………………………………………………………
……………………………………………………………………………………

23
Software Project
Management 2.7 FORMULATING A TASK SET FOR THE
PROJECT

The objective of this section is to get an insight into project scheduling by defining
various task sets dependent on the project and choosing proper tasks for software
engineering.
Various static and dynamic scheduling methods are also discussed for proper
implementation of the project.

Factors affecting the task set for the project

• Technical staff expertise: All staff members should have sufficient technical
expertise for timely implementation of the project. Meetings have to be
conducted, weekly and status reports are to be generated.

• Customer satisfaction : Customer has to be given timely information regarding

the status of the project. If not, there might be a communication gap between the
customer and the organisation.

• Technology update : Latest tools and existing tested modules have to be used for
fast and efficient implementation of the project.

• Full or partial implementation of the project : In case, the project is very large
and to meet the market requirements, the organisation has to satisfy the customer
with at least a few modules. The remaining modules can be delivered at a later
stage.

• Time allocation : The project has to be divided into various phases and time for
each phase has to be given in terms of person-months, module-months, etc.

• Module binding : Module has to bind to various technical staff for design,
implementation and testing phases. Their necessary inter-dependencies have to be
mentioned in a flow chart.

• Milestones : The outcome for each phase has to be mentioned in terms of quality,
specifications implemented, limitations of the module and latest updates that can
be implemented (according to the market strategy).

• Validation and Verification : The number of modules verified according to

customer specification and the number of modules validated according to
customer’s expectations are to be specified.

2.8 CHOOSING THE TASKS OF SOFTWARE

ENGINEERING

Once the task set has been defined, the next step is to choose the tasks for software
project. Depending upon the software process model like linear sequential, iterative,
evolutionary model etc., the corresponding task is selected. From the above task set,
let us consider how to choose tasks for project development (as an example) as
follows:
• Scope : Overall scope of the project.

24
• Scheduling and planning : Scheduling of various modules and their milestones, Risk Management and
preparation of weekly reports, etc. Project Scheduling

• Technology used : Latest hardware and software used.

• Customer interaction : Obtaining feedback from the customer.
• Constraints and limitations : Various constraints in the project and how they can
be solved. Limitations in the modules and how they can be implemented in the
next phase of the project, etc.
• Risk Assessment : Risk involved in the project with respect to limitations in the
technology and resources.

2.9 SCHEDULING METHODS

Scheduling of a software project can be correlated to prioritising various tasks (jobs)
with respect to their cost, time and duration. Scheduling can be done with resource
constraint or time constraint in mind. Depending upon the project, scheduling methods
can be static or dynamic in implementation.

Scheduling Techniques
The following are various types of scheduling techniques in software engineering are:
• Work Breakdown Structure : The project is scheduled in various phases
following a bottom-up or top-down approach. A tree-like structure is followed
without any loops. At each phase or step, milestone and deliverables are
mentioned with respect to requirements. The work breakdown structure shows the
overall breakup flow of the project and does not indicate any parallel flow.
Figure 2.2 depicts an example of a work breakdown structure.

Software Project

Design Coding Testing

Maintenance

Figure 2.2: An example WBS

The project is split into requirement and analysis, design, coding, testing and
maintenance phase. Further, requirement and analysis is divided into R1,R2 ..
Rn; design is divided into D1,D2..Dn; coding is divided into C1,C2..Cn; testing is
divided into T1,T2.. Tn; and maintenance is divided into M1, M2.. Mn. If the project

25
Software Project is complex, then further sub division is done. Upon the completion of each stage,
Management integration is done.

• Flow Graph : Various modules are represented as nodes with edges connecting
nodes. Dependency between nodes is shown by flow of data between nodes.
Nodes indicate milestones and deliverables with the corresponding module
implemented. Cycles are not allowed in the graph. Start and end nodes indicate
the source and terminating nodes of the flow. Figure 2.3 depicts a flow graph.

M2
Start M1
M4 End

M3

Figure 2.3 : Flow Graph

M1 is the starting module and the data flows to M2 and M3. The combined data
from M2 and M3 flow to M4 and finally the project terminates. In certain
projects, time schedule is also associated with each module. The arrows indicate
the flow of information between modules.

• Gantt Chart or Time Line Charts : A Gantt chart can be developed for the
entire project or a separate chart can be developed for each function. A tabular
form is maintained where rows indicate the tasks with milestones and columns
indicate duration ( weeks/months) . The horizontal bars that spans across columns
indicate duration of the task. Figure 2.4 depicts a Gantt Chart. The circles indicate
the milestones.

Tasks Week1 Week2 Week3 Week4

A
i a1
ii a2
Milestone
B
i b1
ii b2
Milestone
C i c1
Milestone
D i d1
ii d2
Milestone

Figure 2.4: Gantt Chart

• Program Evaluation Review Technique : Mainly used for high-risk projects

with various estimation parameters. For each module in a project, duration is
estimated as follows:

1. Time taken to complete a project or module under normal conditions,

tnormal.

26
 2. Time taken to complete a project or module with minimum time (all Risk Management and
resources available), tmin . Project Scheduling

3. Time taken to complete a project or module with maximum time (resource

constraints), tmax.

4. Time taken to complete a project from previous related history,

Thistory.

An average of tnormal, tmin, tmax and thistory is taken depending upon the project.
Sometimes, various weights are added as 4*tnormal, 5*tmin, 0.9*tmax and
2*thistory to estimate the time for a project or module. Parameter fixing is done by the
project manager.

2.10 THE SOFTWARE PROJECT PLAN

Planning is very important in every aspect of development work. Good managers

carefully monitor developments at various phases. Improper planning leads to failure
of the project. Software project plan can be viewed as the following :

1. Within the organisation: How the project is to be implemented? What are various
constraints(time, cost, staff) ? What is market strategy?

2. With respect to the customer: Weekly or timely meetings with the customer with
presentations on status reports. Customer feedback is also taken and further
modifications and developments are done. Project milestones and deliverables are
also presented to the customer.

For a successful software project, the following steps can be followed:

• Select a project
o Identifying project’s aims and objectives
o Understanding requirements and specification
o Methods of analysis, design and implementation
o Testing techniques
o Documentation

• Project milestones and deliverables

• Budget allocation
o Exceeding limits within control

• Project Estimates
o Cost
o Time
o Size of code
o Duration

• Resource Allocation
o Hardware
o Software
o Previous relevant project information
o Digital Library

• Risk Management
o Risk Avoidance
o Risk Detection
27
Software Project o Risk Control
Management o Risk Recovery

• Scheduling techniques
o Work Breakdown Structure
o Activity Graph
o Critical path method
o Gantt Chart
o Program Evaluation Review Technique

• People
o Staff Recruitment
o Team management
o Customer interaction
• Quality control and standard
All of the above methods/techniques are not covered in this unit. The student is
advised to study references for necessary information.

) Check Your Progress 3

1) Mention at least two factors to formulate a task set for a software project.
……………………………………………………………………………
……………………………………………………………………………
2) What are the drawbacks of work breakdown structure?
…….…………………………………………………………………………
…….…………………………………………………………………………
3) What are the advantages of Gantt chart?
…..…………………………………………………………………………
……………………………………………………………………………..
4) What is the purpose of software project plan?
……..………………………………………………………………………
…………………………………………..…………………………………

2.11 SUMMARY
This unit describes various risk management and risk monitoring techniques. In case,
major risks are identified, they are resolved and finally risk recovery is done. Risk
manager takes care of all the phases of risk management. Various task sets are defined
for a project from the customer point of view, the developer’s point of view, the
market strategy view, future trends, etc. For the implementation of a project, a proper
task set is chosen and various attributes are defined. For successful implementation of
a project, proper scheduling (with various techniques) and proper planning are done.

2.12 SOLUTIONS/ANSWERS
Check Your Progress 1
1) Any problem that occurs during customer specification, design, coding,
implementation and testing can be termed as a risk. If they are ignored, then they
propagate further down and it is termed ripple effect. Risk management deals with
avoidance and detection of risk at every phase of the software development cycle.
28
2) Two risks involved with team members are as follows: Risk Management and
Project Scheduling
• Improper training of the technical staff.
• Lack of proper communication between the developers.

3) The organisation should be aware of various competing vendors in the market,

and various risks involved if the product is not delivered on time. It should have
statistics of projects and risks involved from their previous experience or should
have expertise personnel. The organisation should take care that the product will
be able to support upcoming changes in hardware and software platforms.

4) Monitoring of risks means identifying problems in software functions, hardware

deficiencies ( lack of memory , peripherals, fast cpu and so on ), etc. Risk table
has entries for all the risk types and their timely weekly solution . Priorities of
various risks are maintained.

5) Risks can be prioritised upon their dependencies on other modules and external
factors. If a module is having many dependencies then its priority is given higher
value compared to independent modules. If a module often causes security failure
in the system, its priority can be set to a higher value.

Check Your Progress 2

1) Risk management means taking preventive measures for a software project to be

free from various types of risks such as technical, customer, commercial, etc.

2) Various phases of risk management are risk avoidance, risk detection, risk
analysis, risk monitoring, risk control and risk recovery.

3) Attributes mentioned in the risk analysis table are risk name, probability of
occurrence of risk, weight factor and risk exposure.

4) Risk resolution means taking final steps to free the module or system from risk.
Risk resolution involves risk elimination, risk transfer and disclosure of risk to the
customer.

5) Some times, it is difficult to recover from the risk and it is better to add extra
features or an alternate solutions keeping in view of customer specification with
slight modifications in order to match future trends in hardware and software
markets.

Check Your Progress 3

1) The two factors to formulate a task set for a software project are as follows:

• Customer satisfaction
• Full or partial implementation of the project

2) Work breakdown structure does not allow parallel flow design.

3) Gantt chart or time line chart indicates timely approach and milestone for each
task and their relevant sub tasks.

4) Software project plan indicates scope of the project, milestones and deliverables,
project estimates, resource allocation, risk management, scheduling techniques
and quality control and standard .

29
Software Project
Management 2.13 FURTHER READINGS

1) Software Engineering, Ian Sommerville; Sixth Edition, 2001, Pearson Education.

2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman; McGraw-

Hill International Edition.

Reference websites

http://www.rspa.com
http://www.ieee.org
http://www.ncst.ernet.in

30
 Software Quality
Assurance

UNIT 3 SOFTWARE QUALITY ASSURANCE

Structure Page Nos.

3.0 Introduction 31
3.1 Objectives 31
3.2 Software Quality 31
3.3 Formal Technical Review 35
3.4 Software Reliability 40
3.5 Software Quality Standards 41
3.6 Summary 43
3.7 Solutions/Answers 43
3.8 Further Readings 44

3.0 INTRODUCTION

Software quality assurance is a series of activities undertaken throughout the software

engineering process. It comprises the entire gamut of software engineering life cycle.
The objective of the software quality assurance process is to produce high quality
software that meets customer requirements through a process of applying various
procedures and standards.

3. 1 OBJECTIVES

The purpose of this unit is to give an insight as to how software quality assurance
activity is undertaken in the software engineering process.

After studying this unit, you should be able to understand the:

• concepts of Software quality and quality assurance;

• process of a formal technical review in a quality assurance process, and
• concepts of software reliability and software quality standards.

3.2 SOFTWARE QUALITY

Quality is defined as conformance to the stated and implied needs of customer.

Quality also refers to the measurable characteristics of a software product and these
can be compared based on a given set of standards. In the same way, software quality
can be defined as conformance to explicitly stated and implicitly stated functional
requirements. Here, the explicitly stated functional requirement can be derived from
the requirements stated by the customer which are generally documented in some
form. Implicit requirements are requirements which are not stated explicitly but are
intended. Implicit functional requirements are standards which a software
development company adheres to during the development process. Implicit functional
requirements also include the requirements of good maintainability.

Quality software is reasonably bug-free, delivered on time and within budget, meets
requirements and is maintainable. However, as discussed above, quality is a
subjective term. It will depend on who the ‘customer’ is and their overall influence in
the scheme of things. Each type of ‘customer’ will have their own slant on ‘quality’.
The end-user might define quality as some thing which is user-friendly and bug-free.

31
Software Project
Management
Good quality software satisfies both explicit and implicit requirements. Software
quality is a complex mix of characteristics and varies from application to application
and the customer who requests for it.
.
Attributes of Quality

The following are some of the attributes of quality:

Auditability : The ability of software being tested against conformance to standard.

Compatibility : The ability of two or more systems or components to perform their

required functions while sharing the same hardware or software environment.

Completeness: The degree to which all of the software’s required functions and
design constraints are present and fully developed in the requirements specification,
design document and code.

Consistency: The degree of uniformity, standardisation, and freedom from

contradiction among the documents or parts of a system or component.

Correctness: The degree to which a system or component is free from faults in its
specification, design, and implementation. The degree to which software,
documentation, or other items meet specified requirements.

Feasibility: The degree to which the requirements, design, or plans for a system or
component can be implemented under existing constraints.

Modularity : The degree to which a system or computer program is composed of

discrete components such that a change to one component has minimal impact on
other components.

Predictability: The degree to which the functionality and performance of the

software are determinable for a specified set of inputs.

Robustness: The degree to which a system or component can function correctly in

the presence of invalid inputs or stressful environmental conditions.

Structuredness : The degree to which the SDD (System Design Document) and code
possess a definite pattern in their interdependent parts. This implies that the design
has proceeded in an orderly and systematic manner (e.g., top-down, bottom-up). The
modules are cohesive and the software has minimised coupling between modules.

Testability: The degree to which a system or component facilitates the establishment

of test criteria and the performance of tests to determine whether those criteria have
been met.

Traceability: The degree to which a relationship can be established between two or

more products of the development process. The degree to which each element in a
software development product establishes its reason for existing (e.g., the degree to
which each element in a bubble chart references the requirement that it satisfies). For
example, the system’s functionality must be traceable to user requirements.

Understandability: The degree to which the meaning of the SRS, SDD, and code are
clear and understandable to the reader.

Verifiability : The degree to which the SRS, SDD, and code have been written to
facilitate verification and testing.

Causes of error in Software

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 Software Quality
Assurance
• Misinterpretation of customers’ requirements/communication
• Incomplete/erroneous system specification
• Error in logic
• Not following programming/software standards
• Incomplete testing
• Inaccurate documentation/no documentation
• Deviation from specification
• Error in data modeling and representation.

Measurement of Software Quality (Quality metrics)

Software quality is a set of characteristics that can be measured in all phases of

software development.

Defect metrics

• Number of design changes required

• Number of errors in the code
• Number of bugs during different stages of testing
• Reliability metrics
• It measures the mean time to failure (MTTF), that may be defined as probability
of failure during a particular interval of time. This will be discussed in software
reliability.

Maintainability metrics

ƒ Complexity metrics are used to determine the maintainability of software. The

complexity of software can be measured from its control flow.

Consider the graph of Figure 3.1. Each node represents one program segment and
edges represent the control flow. The complexity of the software module represented
by the graph can be given by simple formulae of graph theory as follows:

V(G) = e – n + 2 where

V(G) : is called Cyclomatic complexity of the program

e = number of edges
n = number of nodes

B C

Figure 3.1: A software module

Applying the above equation the complexity V(G) of the graph is found to be 3.

The cyclomatic complexity has been related to programming effort, maintenance

effort and debugging effort. Although cyclomatic complexity measures program
complexity, it fails to measure the complexity of a program without multiple
conditions.

33
Software Project
Management

The information flow within a program can provide a measure for program
complexity.

Important parameters for measurement of Software Quality

• To the extent it satisfies user requirements; they form the foundation to measure
software quality.
• Use of specific standards for building the software product. Standards could be
organisation’s own standards or standards referred in a contractual agreement.
• Implicit requirements which are not stated by the user but are essential for quality
software.

Software Quality Assurance

The aim of the Software Quality Assurance process is to develop high-quality

software product.

The purpose of Software Quality Assurance is to provide management with

appropriate visibility into the process of the software project and of the products
being built. Software Quality Assurance involves reviewing and auditing the software
products throughout the development lifecycle to verify that they conform to explicit
requirements and implicit requirements such as applicable procedures and standards.
Compliance with agreed-upon standards and procedures is evaluated through process
monitoring, product evaluation, and audits.

Software Quality Assurance (SQA) is a planned, coordinated and systematic actions

necessary to provide adequate confidence that a software product conforms to
established technical requirements.

Software Quality Assurance is a set of activities designed to evaluate the process by

which software is developed and/or maintained.

The process of Software Quality Assurance

1. Defines the requirements for software controlled system fault/failure detection,

isolation, and recovery;

2. Reviews the software development processes and products for software error
prevention and/ or controlled change to reduced functionality states; and

3. Defines the process for measuring and analysing defects as well as reliability and
maintainability factors.
Software engineers, project managers, customers and Software Quality Assurance
groups are involved in software quality assurance activity. The role of various groups
in software quality assurance are as follows:

• Software engineers: They ensure that appropriate methods are applied to

develop the software, perform testing of the software product and participate in
formal technical reviews.

• SQA group: They assist the software engineer in developing high quality
product. They plan quality assurance activities and report the results of review.
) Check Your Progress 1
1) What is auditability?
…………………………………………………………………………………
…

34
 Software Quality
Assurance
2) Traceability is the ability of traceacing design back to ____________

3) Software quality is designed in to software and can’t be infused after the

product is released. Explain?
…………………………………………………………………………………
…
…………………………………………………………………………………
…

3.3 FORMAL TECHNICAL REVIEW

What is software Review ? Software review can’t be defined as a filter for the
software engineering process. The purpose of any review is to discover errors in
analysis, design, coding, testing and implementation phase of software development
cycle. The other purpose of review is to see whether procedures are applied
uniformly and in a manageable manner.

Reviews are basically of two types, informal technical review and formal technical
review.

• Informal Technical Review : Informal meeting and informal desk checking.

• Formal Technical Review: A formal software quality assurance activity through
various approaches such as structured walkthroughs, inspection, etc.

What is Formal Technical Review: Formal technical review is a software quality

assurance activity performed by software engineering practitioners to improve
software product quality. The product is scrutinised for completeness, correctness,
consistency, technical feasibility, efficiency, and adherence to established standards
and guidelines by the client organisation.

Structured walkthrough is a review of the formal deliverables produced by the project

team. Participants of this review typically include end-users and management of the
client organization, management of the development organisation, and sometimes
auditors, as well as members of the project team. As such, these reviews are more
formal in nature with a predefined agenda, which may include presentations,
overheads, etc.

An inspection is more formalised than a ‘Structured walkthrough’, typically with 3-8

people. The subject of the inspection is typically a document such as a requirements
specification or a test plan, and the purpose is to find problems and see what’s
missing, not to suggest rectification or fixing. The result of the inspection meeting
should be a written report.

Verification : Verification generally involves reviews to evaluate whether correct

methodologies have been followed by checking documents, plans, code,
requirements, and specifications. This can be done with checklists, walkthroughs, etc.

Validation : Validation typically involves actual testing and takes place after
verifications are completed.

Objectives of Formal Technical Review

• To uncover errors in logic or implementation

• To ensure that the software has been represented accruing to predefined standards
• To ensure that software under review meets the requirements
• To make the project more manageable.

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Software Project
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Each Formal Technical Review (FTR) is conducted as a meeting and requires well
coordinated planning and commitments.

For the success of formal technical review, the following are expected:

• The schedule of the meeting and its agenda reach the members well in advance
• Members review the material and its distribution
• The reviewer must review the material in advance.

The meeting should consist of two to five people and should be restricted to not
more than 2 hours (preferably). The aim of the review is to review the product/work
and the performance of the people. When the product is ready, the producer
(developer) informs the project leader about the completion of the product and
requests for review. The project leader contacts the review leader for the review. The
review leader asks the reviewer to perform an independent review of the
product/work before the scheduled FTR.

Result of FTR

• Meeting decision
o Whether to accept the product/work without any modification
o Accept the product/work with certain changes
o Reject the product/work due to error

• Review summary report

o What was reviewed?
o Who reviewed it?
o Findings of the review
o Conclusion

Checklist - Typical activities for review at each phase are described below:

Software Concept and Initiation Phase

Involvement of SQA team in both writing and reviewing the project management
plan in order to assure that the processes, procedures, and standards identified in the
plan are appropriate, clear, specific, and auditable.

• Have design constraints been taken in to account?

• Whether best alternatives have been selected.

Software Requirements Analysis Phase

During the software requirements phase, review assures that software requirements
are complete, testable, and properly expressed as functional, performance, and
interface requirements. The output of a software requirement analysis phase is
Software Requirements Specification (SRS). SRS forms the major input for review.

Compatibility

• Does the interface enables compatibility with external interfaces?

• Whether the specified models, algorithms, and numerical techniques are
compatible?

Completeness

• Does it include all requirements relating to functionality, performance, system

constraints, etc.?
• Does SRS include all user requirements?

36
 Software Quality
Assurance
• Are the time-critical functions defined and identified?
• Are the requirements consistent with available resources and budget?
• Does the SRS include requirements for anticipated future changes?

Consistency

• Are the requirements consistent with each other? Is the SRS free of
contradictions?
• Whether SRS uses standard terminology and definitions throughout.
• Has the impact of operational environment on the software been specified in the
SRS?

Correctness

• Does the SRS conform to SRS standards?

• Does the SRS define the required responses to all expected types of errors and
failure? hazard analysis?
• Were the functional requirements analysed to check if all abnormal situations are
covered by system functions?
• Does SRS reference development standards for preparation?
• Does the SRS identify external interfaces in terms of input and output
mathematical variables?
• Has the rationale for each requirement been defined?
• Are the requirements adequate and correctly indicated?
• Is there justification for the design/implementation constraints?

Traceability

• Are the requirements traceable to top level?

• Is there traceability from the next higher level of specification?
• Is SRS traceable forward through successive software development phases like
the design, coding and testing ?

Verifiability and Testability

• Are validation criteria complete?

• Is there a verification procedure defined for each requirement in the SRS?
• Are the requirements verifiable?

Software Design Phase

Reviewers should be able to determine whether or not all design features are
consistent with the requirements. And, the program should meet the requirements.
The output of the software design phase is a system design document (SDD) and
forms an input for a Formal Technical Review.

Completeness

• Whether all the requirements have been addressed in the SDD?

• Have the software requirements been properly reflected in software architecture?
• Are algorithms adequate, accurate, and complete?
• Does the design implement the required program behavior with respect to each
program interface?
• Does the design take into consideration all expected conditions?
• Does the design specify appropriate behaviour in case of an unexpected or
improper input and other abnormal conditions?

Consistency

37
Software Project
Management
• Are standard terminology and definitions used throughout the SDD? Is the style
of presentation and the level of detail consistent throughout the document.
• Does the design configuration ensure integrity of changes?
• Is there compatibility of the interfaces?
• Is the test documentation compatible with the test requirements of the SRS?
• Are the models, algorithms, and numerical techniques that are specified
mathematically compatible?
• Are input and output formats consistent to the extent possible?
• Are the designs for similar or related functions are consistent?
• Are the accuracies and units of inputs, database elements, and outputs that are
used together in computations or logical decisions compatible?

Correctness

• Does the SDD conform to design documentation standards?

• Does the design perform only that which is specified in the SRS?
• Whether additional functionality is justified?
• Is the test documentation current and technically accurate?
• Is the design logic sound i.e., will the program do what is intended?
• Is the design consistent with documented descriptions?
• Does the design correctly accommodate all inputs, outputs, and database elements ?

Modifiability

• The modules are organised such that changes in the requirements only require
changes to a small number of modules.
• Functionality is partitioned into programs to maximize the internal cohesion of
programs and to minimize program coupling.
• Is the design structured so that it comprises relatively small, hierarchically related
programs or sets of programs, each performing a particular unique function?
• Does the design use a logical hierarchical control structure?

Traceability

• Is the SDD traceable to requirements in SRS?

• Does the SDD show mapping and complete coverage of all requirements and
design constraints in the SRS?
• Whether the functions in the SDD which are outside the scope of SRS are defined
and identified?

Verifiability

• Does the SDD describe each function using well-defined notation so that the
SDD can be verified against the SRS
• Can the code be verified against the SDD?
• Are conditions, constraints identified so that test cases can be designed?

Review of Source Code

The following checklist contains the kinds of questions a reviewer may take up
during source code review based on various standards

Completeness

• Is the code complete and precise in implementation?

• Is the code as per the design documented in the SDD?
• Are there any unreferenced or undefined variables, constants, or data types?
• Whether the code follows any coding standard that is referenced?

38
 Software Quality
Assurance
Consistency

• Is the code consistent with the SDD?

• Are the nomenclature of variables, functions uniform throughout?

Correctness

• Does the code conform to specified coding standards?

• Are all variables properly specified and used?
• Does the code avoid recursion?
• Does the code protect against detectable runtime errors?
• Are all comments accurate and sufficient?
• Is the code free of unintended infinite loops?

Modifiability

• Is the program documentation sufficient to facilitate future changes?

• Does the code refer to constants symbolically so as to facilitate change?
• Is the code written in a language with well-defined syntax and semantics?
• Are the references or data dictionaries included to show variable and constant
access by the program?
• Does the code avoid relying on defaults provided by the programming language?

Traceability

• Is the code traceable to design document?

• Does the code identify each program uniquely?
• Is there a cross-reference through which the code can be easily and directly traced
to the SDD?
• Does the code contain, or has reference to, a revision history of all code
modifications done by different authors?
• Whether the reasons for such modification are specified and authorized?

Understandability

• Do the comment statements in the code adequately describe each routine?

• Whether proper indent and formatting has been used to enhance clarity?
• Has the formatting been used consistently?
• Does naming patterns of the variables properly reflect the type of variable?
• Is the valid range of each variable defined?

Software Testing and Implementation Phase

• Whether all deliverable items are tested.
• Whether test plans are consistent and sufficient to test the functionality of the
systems.
• Whether non-conformance reporting and corrective action has been initiated?.
• Whether boundary value is being tested.
• Whether all tests are run according to test plans and procedures and any non-
conformances are reported and resolved?
• Are the test reports complete and correct?
• Has it been certified that testing is complete and software including
documentation are ready for delivery?

Installation phase

Completeness

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Software Project
Management
• Are the components necessary for installation of a program in this installation
medium ?
• Whether adequate information for installing the program, including the system
requirements for running the program available.
• Is there more than one operating environment?
• Are installation procedures for different running environments available?
• Are the installation procedures clearly understandable?

) Check Your Progress 2

1) The purpose of review is to uncover errors and non conformity during testing
phase. Yes No
2) The result of a review does not include
a) The items that are to be reviewed
b) The person who reviews it
c) Findings of the review
d) Solution to a problem

3) What could become an input for FTR in design phase?

……………………………………………………………………………………
……………………………………………………………………………………
……

3.4 SOFTWARE RELIABILITY

Software Reliability: Unlike reliability of the hardware device, the term software
reliability is difficult to measure. In the software engineering environment, software
reliability is defined as the probability that software will provide failure-free
operation in a fixed environment for a fixed interval of time.

Software reliability is typically measured per a unit of time, whereas probability of

failure is generally time independent. These two measures can be easily related if you
know the frequency with which inputs are executed per unit of time. Mean-time-to-
failure (MTTF) is the average interval of time between failures; this is also
sometimes referred to as Mean-time-before-failure.

Possibly the greatest problem in the field of software reliability estimation has to do
with the accuracy of operational profiles. Without accurate profiles, estimates will
almost certainly be wrong. An operational profile is the probability density function
(over the entire input space) that best represents how the inputs would be selected
during the life-time of the software. There is nothing fancy about operational profiles;
they are really just “guesses” about what inputs will occur in the future.

Definitions of Software reliability

• IEEE Definition: The probability that software will not cause the failure of a
system for a specified time under specified conditions. The probability is a
function of the inputs to and use of the system in the software. The inputs to the
system determine whether existing faults, if any, are encountered.

• The ability of a program to perform its required functions accurately and

reproducibly under stated conditions for a specified period of time.

Software Reliability Models

A number of models have been developed to determine software defects/failures. All

these models describe the occurrence of defects/failures as a function of time. This

40
 Software Quality
Assurance
allows us to define reliability. These models are based on certain assumptions which
can be described as below:

• The failures are independent of each other, i.e., one failure has no impact on other
failure(s).
• The inputs are random samples.
• Failure intervals are independent and all software failures are observed.
• Time between failures is exponentially distributed.

The following formula gives the cumulative number of defects observed at a time ‘t’.

D(t) = Td (1 – e –bct)

D(t) = Cumulative number of defects observed at a time t

Td = Total number of defects

‘b’ and ‘c’ are constants and depend on historical data of similar software for which
the model is being applied

We may find the mean time to failure (MMFT) as below:

MTTF(t) = e bct / c Td

3.5 SOFTWARE QUALITY STANDARDS

Software standards help an organization to adopt a uniform approach in designing,

developing and maintaining software. There are a number of standards for software
quality and software quality assurance. Once an organisation decides to establish a
software quality assurance process, standards may be followed to establish and
operate different software development activities and support activities. A number of
organisations have developed standards on quality in general and software quality in
specific.

Software Engineering Institute (SEI) has developed what is called a ‘Capability

Maturity Model’ (CMM) now called the Capability Maturity Model Integration
(CMMI) to help organisations to improve software development processes.

It is a model of 5 levels of process maturity that determine the effectiveness of an

organisation in delivering quality software. Organizations can receive CMMI ratings
by undergoing assessments by qualified auditors. The organizations are rated as
CMM Level 1, CMM Level 2 etc. by evaluating their organisational process maturity.

SEI-CMM Level 1: Characterised by un organised, chaos, periodic panics, and heroic

efforts required by individuals to successfully complete projects. Successes depend
on individuals and may not be repeatable.

SEI-CMM Level 2 : Software project tracking, requirements management, realistic

planning, and configuration management processes are in place; successful practices
can be repeated.
SEI-CMM Level 3: Standard software development and maintenance processes are
integrated throughout an organisation; a Software Engineering Process Group is in
place to oversee software processes, and training programs are used to ensure
understanding and compliance.

SEI-CMM Level 4: Metrics are used to track productivity, processes, and products.
Project performance is predictable, and quality is consistently high.

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Software Project
Management

SEI-CMM Level 5: The focus is on continuous process improvement. The impact of

new processes and technologies can be predicted and effectively implemented when
required.
The International Organisation for Standardisation (ISO) developed the ISO
9001:2000 standard (which replaces the previous set of three standards of 1994) that
helps the organisation to establish, operate, maintain and review a quality
management system that is assessed by outside auditors. The standard is generic in
nature and can be applied to any organisation involved in production, manufacturing
service including an organisation providing software services.

It covers documentation, design, development, production, testing, installation,

servicing, and other processes. It may be noted that ISO certification does not
necessarily indicate quality products. It only indicates that the organisation follows a
well documented established process. Table 3.1 gives a list of standards along with
the corresponding titles.
Table 3.1 : List of standards
Standards Title
ISO/IEC 90003 Software Engineering. Guidelines for the Application of ISO 9001:2000 to
Computer Software
ISO 9001:2000 Quality Management Systems - Requirements

ISO/IEC 14598-1 Information Technology-Evaluation of Software Products-General Guide

ISO/IEC 9126-1 Software Engineering - Product Quality - Part 1: Quality Model

ISO/IEC 12119 Information Technology-Software Packages-Quality Requirements and

Testing
ISO/IEC 12207 Information Technology-Software Life Cycle Processes

ISO/IEC 14102 Guideline For the Evaluation and Selection of CASE Tools
IEC 60880 Software for Computers in the Safety Systems of Nuclear Power Stations

IEEE 730 Software Quality Assurance Plans

IEEE 730.1 Guide for Software Assurance Planning

IEEE 982.1 Standard Dictionary of Measures to produce reliable software
IEEE 1061 Standard for a Software Quality Metrics Methodology
IEEE 1540 Software Life Cycle Processes - Risk Management
IEEE 1028 Software review and audits
IEEE 1012 Software verification and validation plans

) Check Your Progress 3

1) Success of a project depends on individual effort. At what stage of maturity does
the organisation’s software process can be rated?
………………………………………………………………………………………………..
………………………………………………………………………………………………...
2) Why ISO 9001 : 2000 is called generic standard?
……………………………………………………………………………………..
……………………………………………………………………………………..

3) What is the difference between SEI CMM standards and ISO 9000 : 2000 standards?
……………………………………………………………………………………
…
……………………………………………………………………………………
…

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 Software Quality
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3.6 SUMMARY

Software quality assurance is applied at every stages of system development through

a process of review to ensure that proper methodology and procedure has been
followed to produce the software product. It covers the entire gamut of software
development activity. Software quality is conformance with explicitly defined
requirements which may come from a customer requirement or organisation may
define their own standards. Software review also called a Formal Technical Review is
one of the most important activity of software quality assurance process. Software
reliability provides measurement of software dependability and probability of failure
is generally time independent. The aim of software quality assurance is to improve
both software product and process through which the software is built. The help of
various software standards taken to establish and operate software quality assurance
process.

3.7 SOLUTIONS/ANSWERS

Check Your Progress 1

1) Auditabality is that attribute of software which determines the degree to which a

software can be tested for conformance against a standard.

2) Requirements.

3) Software quality assurance activity is an umbrella activity comprising activities

like application of standards, technical methods, review, software testing, change
control, measurement, control & reporting during the process of software
development life cycle. High quality product can come from high quality design
specification. Unlike quality, testing quality assurance can’t be achieved at the
end of the product completion phase.

Check Your Progress 2

1) No. The purpose of any review is to discover errors in the analysis, design,
coding, testing and maintenance phases of software development life cycle.

2) Solution to a problem.

3) Output of the software design phase is a system design document (SDD) and it is
an input for the Formal Technical Review.
Check Your Progress 3

1) SEI CMM level 1.

2) The standards are called generic in nature as they can be applied to any
organisation involved in the production, manufacturing service including
organisations providing software services which involve no manufacturing
process.
3) SEI CMM standards are developed to rate the maturity of organisation’s software
development process. The maturity is rated from level 1 to level 5, i.e., from
immature (no formal process) to predictable matured process with focus on
continuous improvement. In case of ISO 9001 : 2000, the organisation’s process
(quality system) is tested against conformance to the requirements of
ISO 9000 : 2000 standard.

3.8 FURTHER READINGS

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Software Project
Management

1) Software Quality, 1997, Mordechai Ben-Menachem and Garry S.Marliss;

Thomson Learning.

2) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson

Education.

3) Software Engineering – A Practitioner’s Approach, Roger S. Pressman;

McGraw-Hill International Edition.

Reference websites

http://www.rspa.com
http://www.ieee.org

44
 Software Change
UNIT 4 SOFTWARE CHANGE Management

MANAGEMENT
Structure Page Nos.

4.0 Introduction 45
4.1 Objectives 45
4.2 Baselines 45
4.3 Version Control 48
4.4 Change Control 51
4.5 Auditing and Reporting 54
4.6 Summary 56
4.7 Solutions/Answers 56
4.8 Further Readings 56

4.0 INTRODUCTION
Software change management is an umbrella activity that aims at maintaining the
integrity of software products and items. Change is a fact of life but uncontrolled
change may lead to havoc and may affect the integrity of the base product. Software
development has become an increasingly complex and dynamic activity. Software
change management is a challenging task faced by modern project managers,
especially in a environment where software development is spread across a wide
geographic area with a number of software developers in a distributed environment.
Enforcement of regulatory requirements and standards demand a robust change
management. The aim of change management is to facilitate justifiable changes in the
software product.

4.1 OBJECTIVES

After studying this unit, you should be able to:

• define baselines;
• know the concept of version control and change control, and
• audit and report software change management activity.

4.2 BASELINES

Baseline is a term frequently used in the context of software change management.

Before we understand the concept of baseline, let us define a term which is called
software configuration item. A software configuration item is any part of development
and /or deliverable system which may include software, hardware, firmware,
drawings, inventories, project plans or documents. These items are independently
tested, stored, reviewed and changed. A software configuration item can be one or
more of the following:

• System specification
• Source code
• Object code
• Drawing
• Software design
45
Software Project • Design data
Management • Database schema and file structure
• Test plan and test cases
• Product specific documents
• Project plan
• Standards procedures
• Process description

Definition of Baseline: A baseline is an approved software configuration item that has

been reviewed and finalised. An example of a baseline is an approved design
document that is consistent with the requirements. The process of review and approval
forms part of the formal technical review. The baseline serves as a reference for any
change. Once the changes to a reference baseline is reviewed and approved, it acts as
a baseline for the next change(s).

A baseline is a set of configuration items (hardware, documents and software

components) that have been formally reviewed and agreed upon, thereafter serve as
the basis for future development, and that can be changed only through formal change
control procedures.

Figure 4.1 depicts a baseline for design specification.

Design Review Reviewed

specification approval
design Baseline
Error specification
correction

Figure 4.1 : A baseline for design specification

Figure 4.2 depicts the evolution of a baseline.

approved approved
Baseline 1 changes Baseline 2 changes Baseline 3

Figure 4.2: Evolution of a baseline

A baseline is functionally complete, i.e., it has a defined functionality. The features of

these functionalities are documented for reference for further changes. The baseline
has a defined quality which has undergone a formal round of testing and reviews
before being termed as a baseline. Any baseline can be recreated at any point of time.

The process of change management

The domain of software change management process defines how to control and
manage changes.

46
A formal process of change management is acutely felt in the current scenario when Software Change
the software is developed in a very complex distributed environment with many Management
versions of a software existing at the same time, many developers involved in the
development process using different technologies. The ultimate bottomline is to
maintain the integrity of the software product while incorporating changes.

The following are the objectives of software change management process:

1. Configuration identification: The source code, documents, test plans, etc.

The process of identification involves identifying each component name,
giving them a version name (a unique number for identification) and a
configuration identification.
2. Configuration control: Cntrolling changes to a product. Controlling release
of a product and changes that ensure that the software is consistent on the
basis of a baseline product.
3. Review: Reviewing the process to ensure consistency among different
configuration items.
4. Status accounting : Recording and reporting the changes and status of the
components.
5. Auditing and reporting: Validating the product and maintaining consistency
of the product throughout the software life cycle.

Process of changes: As we have discussed, baseline forms the reference for any
change. Whenever a change is identified, the baseline which is available in project
database is copied by the change agent (the software developer) to his private area.
Once the modification is underway the baseline is locked for any further modification
which may lead to inconsistency. The records of all changes are tracked and recorded
in a status accounting file. After the changes are completed and the changes go
through a change control procedure, it becomes a approved item for updating the
original baseline in the project database.

Figure 4.3 depicts the process of changes to a baseline.

Project data Private work

base area of
developer
B B’

Configuration
status
accounting file

Figure 4.3: Process of changes to baseline

All the changes during the process of modification are recorded in the configuration
status accounting file. It records all changes made to the previous baseline B to reach
the new baseline B’. The status accounting file is used for configuration authentication
which assures that the new baseline B’ has all the required planned and approved
changes incorporated. This is also known as auditing.
47
Software Project ) Check Your Progress 1
Management
1) _______ serves as reference for any change.

2) What is the aim of software change management process?

……………………………………………………………………………………...
……………………………………………………………………………………...

4.3 VERSION CONTROL

Version control is the management of multiple revisions of the same unit of item
during the software development process. For example, a system requirement
specification (SRS) is produced after taking into account the user requirements which
change with time into account. Once a SRS is finalized, documented and approved, it
is given a document number, with a unique identification number. The name of the
items may follow a hierarchical pattern which may consist of the following:

• Project identifier
• Configuration item (or simply item, e.g. SRS, program, data model)
• Change number or version number

The identification of the configuration item must be able to provide the relationship
between items whenever such relationship exists.

The identification process should be such that it uniquely identifies the configuration
item throughout the development life cycle, such that all such changes are traceable to
the previous configuration. An evolutionary graph graphically reflects the history of
all such changes. The aim of these controls is to facilitate the return to any previous
state of configuration item in case of any unresolved issue in the current unapproved
version.

Ver
1.4

Ver
1.3

Ver Ver Ver

1.0 1.1 1.2 Ver Ver
1.3.1 1.3..2

Ver Ver
2.0 2.1

Figure 4.4 : An evolutionary graph for a different version of an item

The above evolutionary graph(Figure 4.4) depicts the evolution of a configuration

item during the development life cycle. The initial version of the item is given version
number Ver 1.0. Subsequent changes to the item which could be mostly fixing bugs or
adding minor functionality is given as Ver 1.1 and Ver 1.2. After that, a major
modification to Ver 1.2 is given a number Ver 2.0 at the same time, a parallel version
of the same item without the major modification is maintained and given a version
number 1.3.
48
Depending on the volume and extent of changes, the version numbers are given by the Software Change
version control manager to uniquely identify an item through the software Management
development lifecycle. It may be noted that most of the versions of the items are
released during the software maintenance phase.

Software engineers use this version control mechanism to track the source code,
documentation and other configuration items. In practice, many tools are available to
store and number these configuration items automatically. As software is developed
and deployed, it is common to expect that multiple versions of the same software are
deployed or maintained for various reasons. Many of these versions are used by
developers to privately work to update the software.

It is also sometimes desirable to develop two parallel versions of the same product
where one version is used to fix a bug in the earlier version and other one is used to
develop new functionality and features in the software. Traditionally, software
developers maintained multiple versions of the same software and named them
uniquely by a number. But, this numbering system has certain disadvantages like it
does not give any idea about a nearly identical versions of the same software which
may exist.

The project database maintains all copies of the different versions of the software and
other items. It is quite possible that without each other’s knowledge, two developers
may copy the same version of the item to their private area and start working on it.
Updating to the central project database after completing changes will lead to
overwriting of each other’s work. Most version control systems provide a solution to
this kind of problem by locking the version for further modification.

Commercial tools are available for version control which performs one or more of
following tasks;

• Source code control

• Revision control
• Concurrent version control

There are many commercial tools like Rational ClearCase, Microsoft Visual
SourceSafe and a number of other commercial tools to help version control.

Managing change is an important part of computing. The programmer fixes bugs

while producing a new version based on the feedback of the user. System
administrator manages various changes like porting database, migrating to a new
platform and application environment without interrupting the day to day operations.
Revisions to documents are carried out while improving application.

An example of revision control

Let us consider the following simple HTML file in a web based application
(welcome.htm)

<html>
<head>
<Title> A simple HTML Page</title>
</head>
<body>
<h1> Welcome to HTML Concepts</h1>
</body>
</html>

49
Software Project Once the code is tested and finalized, the first step is to register the program to he
Management project database. The revision is numbered and this file is marked read-only to prevent
any further undesirable changes. This forms the building block of source control. Each
time the file is modified, a new version is created and a new revision number is given.

The first version of the file is numbered as version 1.0. Any further modification is
possible only in the developer’s private area by copying the file from the project

database. The process of copying the configuration object (the baseline version) is
called check-out.

Figure 4.5 depicts the changes to a baselined file in project database.

Check-out
Project Developer
database private area
Check-in

Figure 4.5: Changes to a baselined file in project database

The version (revision) control process starts with registering the initial versions of the
file. This essentially enforces a check on the changes which ensure that the file can’t
be changed unless it is checked-out from the project database.

When a change is required to be made, allowing an email address to be added to the

above html file, the developer will extract the latest version of the file welcome.htm
from the project database. Once it is checked-out from the project database for
modification, the file is locked for further modifications by any other developer.
Other developers can check-out the file for read-only purpose.

Now, the following lines are added to the file welcome.htm.

<hr>
a href=mailto:webmaster@xyz.com> webmaster</a>
<hr>

The revised version of the file welcome.htm become

<html>
<head>
<Title> A simple HTML Page</title>
</head>
<body>
<h1> Welcome to HTML Concepts</h1>
<hr>
a href=mailto:webmaster@xyz.com> webmaster</a>
<hr>
</body>
</html>

Then the developer check-in’s the revised version of the file to the project database
with a new version (revision) number version 1.1 i.e. the first revision along with the
details of the modification done.

Suppose another modification is done by adding a graphic to the html file

welcome.htm. This becomes version 1.2. The version tree after two modifications
looks as shown below (Figure 4.6).
50
 Software Change
Management
Ver Ver Ver
1.0 1.1 1.2

Figure 4.6: Version tree of welcome.htm

Suppose further modification is required for text-based browser as graphic will not be
supported by text-based browser. Then the version 1.1 will be selected from the
project database. This shows the necessity of storing all versions of the file in the
project database.

) Check Your Progress 2

1) _______ is an example of source code control tool.

2) Version control mechanism allows multiple versions of an item to be maintained

at the same time. (Yes/No)

3) How do version control systems ensure that two software developers do not
attempt the same change at the same time?
………………………………………………………………………………………
……………………………………………………………………………………...

4.4 CHANGE CONTROL

Change is a fact of life, and the same applies to software development. Although, all
changes requested by the user are not justified changes, but most of them are. The real
challenge of change manager and project leader is to accept and accommodate all
justifiable changes without affecting the integrity of product or without any side
effect. The central to change management process is change control which deals with
the formal process of change control.

The adoption and evolution of changes are carried out in a disciplined manner. In a
large software environment where, as changes are done by a number of software
developers, uncontrolled and un-coordinated changes may lead to havoc grossly
diverting from the basic features and requirements of the system. For this, a formal
change control process is developed.

Change control is a management process and is to some extent automated to provide a

systematic mechanism for change control. Changes can be initiated by the user or
other stake holder during the maintenance phase, although a change request may even
come up during the development phase of the software.

A change request starts as a beginning of any change control process. The change
request is evaluated for merits and demerits, and the potential side effects are
evaluated. The overall impact on the system is assessed by the technical group
consisting of the developer and project manager. A change control report is
generated by the technical team listing the extent of changes and potential side effects.
A designated team called change control authority makes the final decision, based on
the change control report, whether to accept or reject the change request.

A change order called engineering change order is generated after the approval of the
change request by the change control authority. The engineering change order forms
the starting point of effecting a change in the component. If the change requested is
51
Software Project not approved by the change control authority, then the decision is conveyed to the user
Management or the change request generator.

Once, change order is received by the developers, the required configuration items are
identified which require changes. The baseline version of configuration items are
copied from the project data base as discussed earlier.
The changes are then incorporated in the copied version of the item. The changes are
subject to review (called audit) by a designated team before testing and other quality
assurance activity is carried out. Once the changes are approved, a new version is
generated for distribution.

The change control mechanisms are applied to the items which have become
baselines. For other items which are yet to attain the stage of baseline, informal
change control may be applied. For non- baseline items, the developer may make
required changes as he feels appropriate to satisfy the technical requirement as long as
it does not have an impact on the overall system.

The role of the change control authority is vital for any item which has become a
baseline item. All changes to the baseline item must follow a formal change control
process.

As discussed, change request, change report and engineering change order (change
order) are generated as part of the change control activity within the software change
management process. These documents are often represented inprinted or electronic
forms. The typical content of these documents is given below:

Software Change Request Format

1.0 Change request Identification

1.1 Name, identification and description of software configuration item(s):

The name, version numbers of the software configuration is provided. Also, a
brief description of the configuration item is provided.

1.2 Requester and contact details: The name of the person requesting the change
and contact details

1.3 Date, location, and time when the change is requested

2.0 Description of the change

2.1 Description : This section specifies a detailed description of the change

request.

2.1.1 Background Information, Background information of the request.

2.1.2 Examples: Supporting information, examples, error report, and screen
shoots
2.1.3 The change : A detailed discussion of the change requested.

2.2 Justification for the change : Detailed justification for the request.

2.3 Priority : The priority of the change depending on critical effect on system
functionalities.
52
Software Change Report Format Software Change
Management

1.0 Change report Identification

1.1 Name, identification and description of software configuration item(s): The

name, version numbers of the software configuration item and a brief
description of it.

1.2 Requester: The name and contact details of the person requesting the change.

1.3 Evaluator : The name of the person or team who evaluated the change request.

1.4 Date and time : When change report was generated.

2.0 Overview of changes required to accommodate request

2.1 Description of software configuration item that will be affected

2.2 Change categorization : Type of change, in a generic sense

2.3 Scope of the change : The evaluator's assessment of the change.

2.3.1 Technical work required including tools required etc. A description of

the work required to accomplish the change including required tools
or other special resources are specified here

2.3.2 Technical risks : The risks associated with making the change are
described.

3.0 Cost Assessment : Cost assessment of the requested change including an

estimate of time required.

4.0 Recommendation

4.1 Evaluator’s recommendation : This section presents the evaluator's

recommendation regarding the change

4.2 Internal priority: How important is this change in the light of the business
operation and priority assigned by the evaluator.

Engineering Change Order Format

1.0 Change order Identification

1.1 Name, identification and description of software configuration item(s) : The

name, version numbers including a brief description of software configuration
items is provided.

1.2 Name of Requester

1.3 Name of Evaluator

2.0 Description of the change to be made

2.1 Description of software configuration(s) that is affected

53
Software Project 2.2 Scope of the change required
Management
The evaluator's assessment of scope of the change in the configuration item(s).

2.2.1 Technical work and tools required : A description of the work and tools
required to accomplish the change.

2.3 Technical risks: The risks associated with making the change are described in
this section.

3.0 Testing and Validation requirements

A description of the testing and review approach required to ensure that the change
has been made without any undesirable side effects.

3.1 Review plan : Description of reviews that will be conducted.

3.2 Test plan

Description of the test plans and new tests that are required.

Benefits of change control management

The existence of a formal process of change management helps the developer to

identify the responsibility of code for which a developer is responsible. An idea is
achieved about the changes that affect the main product. The existence of such
mechanism provides a road map to the development process and encourages the
developers to be more involved in their work.

Version control mechanism helps the software tester to track the previous version of
the product, thereby giving emphasis on testing of the changes made since the last
approved changes. It helps the developer and tester to simultaneously work on
multiple versions of the same product and still avoid any conflict and overlapping of
activity.

The software change management process is used by the managers to keep a control
on the changes to the product thereby tracking and monitoring every change. The
existence of a formal process reassures the management. It provides a professional
approach to control software changes.

It also provides confidence to the customer regarding the quality of the product.

4.5 AUDITING AND REPORTING

Auditing

Auditing and Reporting helps change management process to ensure whether the
changes have been properly implemented or not, whether it has any undesired impact
on other components. A formal technical review and software configuration audit
helps in ensuring that the changes have been implemented properly during the change
process.

A Formal Technical Review generally concentrates on technical correctness of the

changes to the configuration item whereas software configuration audit complements
it by checking the parameters which are not checked in a Formal Technical Review.
54
A check list for software configuration audit Software Change
Management
• Whether a formal technical review is carried out to check the technical accuracy
of the changes made?

• Whether the changes as identified and reported in the change order have been
incorporated?

• Have the changes been properly documented in the configuration items?

• Whether standards have been followed.

• Whether the procedure for identifying, recording and reporting changes has been
followed.

As it is a formal process, it is desirable to conduct the audit by a separate team other

than the team responsible for incorporating the changes.

Reporting: Status reporting is also called status accounting. It records all changes that
lead to each new version of the item. Status reporting is the bookkeeping of each
release. The process involves tracking the change in each version that leads the
latest(new) version.

The report includes the following:

• The changes incorporated
• The person responsible for the change
• The date and time of changes
• The effect of the change
• The reason for such changes (if it is a bug fixing)

Every time a change is incorporated it is assigned a unique number to identify it from

the previous version. Status reporting is of vital importance in a scenario where a large
number of developers work on the same product at the same time and have little idea
about the work of other developers.
For example, in source code, reporting the changes may be as below:
*********************************************************************
*********************************************************************
*********************************************************************

# Title : Sub routine Insert to Employee Data

# Version : Ver 1.1.3
# Purpose : To insert employee data in the master file
# Author : John Wright
# Date : 23/10/2001
# Auditor : J Waltson
# Modification History:
12/12/2002 : by D K N
To fix bugs discovered in the first release
4/5/2003 : by S K G
to allow validation in date of birth data
6/6/2004 : by S S P
To add error checking module as requested by the customer
55
Software Project ) Check Your Progress 3
Management
1) Who decides the acceptance of a change request?.
……………………………………………………………………………………
……………………………………………………………………………………

2) How auditing is different from a Formal Technical Review (FTR)?

……………………………………………………………………………………
……………………………………………………………………………………

4.6 SUMMARY

Software change management is an activity that is applied throughout the software

development life cycle. The process of change management includes configuration
identification, configuration control, status reporting and status auditing.
Configuration identification involves identification of all configurations that require
changes. Configuration or change control is the process of controlling the release of
the product and the changes. Status accounting or reporting is the process of recording
the status of each component. Review involves auditing consistency and completeness
of the component.

4.7 SOLUTIONS/ANSWERS
Check Your Progress 1
1) Baseline.
2) The domain of software change management process defines how to control and
manage changes. The ultimate aim is to maintain the integrity of the software
product while incorporating changes.
Check Your Progress 2
1) Microsoft Visual SourceSafe
2) Yes
3) Version control system locks the configuration item once it is copied from project
database for modification by a developer.

Check Your Progress 3

1) Change control authority
2) Formal Technical Review is a formal process to evaluate the technical accuracy of
any process or changes. Whereas software change or audit is carried out by a
separate team to ensure that proper change management procedure has been
followed to incorporate the changes.

4.8 FURTHER READINGS

1) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson Education.
2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman; McGraw-
Hill International Edition.
Reference websites
http://www.rspa.com
http://www.ieee.org
56
Software Change
Management

57
 Web Software
UNIT 1 WEB SOFTWARE ENGINEERING Engineering

Structure Page Nos.

1.0 Introduction 5
1.1 Objectives 6
1.2 Different Characteristics 6
1.2.1 Characteristics of a Web Application
1.2.2 Development, Testing and Deployment
1.2.3 Usage of Web Applications
1.2.4 Maintaining Web Applications
1.2.5 Designing Web Applications
1.3 Issues of Management of Web Based Projects 9
1.3.1 Review of Good Software Development Practices
1.3.2 Organisation of Web Application Teams
1.3.3 Development and Maintenance Issues
1.4 Metrics 16
1.5 Analysis 17
1.6 Design and Construction 18
1.7 Reviews and Testing 19
1.8 Summary 20
1.9 Solutions/Answers 21
1.10 Further Reading 21

1.0 INTRODUCTION
Today’s Internet age has brought about a large demand for services that can be
delivered over the network. These services rely in large measure on web software
applications that can be accessed concurrently by many users. Increasing competition
has meant that vendors want shorter and shorter cycle times for producing new
products in any sphere, but in the arena of web based services, the situation is
extreme. Instead of years or even months, new applications have to be readied and
deployed in weeks, before someone else does so. Such pressures are compounded by
the need to have high quality software as no one will visit a buggy website for the
second time.

Besides technical challenges of architecture and design, web software brings in

difficulties caused by the peculiarly distributed nature of the whole endeavour. Not
only is the architecture such that the different tiers could be working out of potentially
different machines located widely apart, the users are likely to be geographically
separated by vast distances and could come from different cultural backgrounds. And,
as likely as not, the development team could be spread out in space and these greatly
separated team members being responsible for the software produced.
Web software could be –
• Meant for the Internet, with users coming from the public in a geographical
region that could perhaps be the whole world.
• Meant for a closed group such as a corporation, in which case, it would be
running over an Intranet.
• Meant for an extended, but still closed groups such as corporations, its
customers and suppliers, where upon it is an Extranet.
Irrespective of the type of usage intended, the users could be separated by large
distances and the application needs to behave correctly for all of them. In this unit,
we will concentrate on web applications meant for the Internet.
We will also explore the difficulties associated with developing and managing a web
based software project. Also examined will be some approaches and general rules
5
Advanced Software that could help us to do such a project well. Please be aware that the subject is vast,
Engineering
and in this short unit we can only touch upon the complexities of the topic.

1.1 OBJECTIVES
After going through this unit, you should be able to:

• identify the characteristics of a web based software application;

• describe the architecture of such an application;
• identify the challenges of managing a web based software project;
• think up relevant metrics to gauge the health of such a project;
• ensure proper understanding of the requirements in such a project so that
development can be pursued, and
• facilitate quality control of a web based project.

1.2 DIFFERENT CHARACTERISTICS

While web based software applications can vary a lot in size and complexity, all of
them share common characteristics, some of which are peculiar to them and are not
prominent in other applications. We can look at these characteristics in terms of–

• The way the applications are developed, tested and deployed

• The way the applications are used
• The way they are maintained
• The design of these applications.

1.2.1 Characteristics of a Web Application

In this section, we will look at the overall architecture and deployment context of web
based applications and see how this leads to their peculiar management challenges.
Unlike conventional applications that can be monolithic, web applications are by their
very nature amenable to layering. One cannot have a monolithic web application as
the client and the rest of the application have to be of necessity separated. In
principle, one could have a thick client application with a lot of intelligence embedded
at the client end, but that would defeat the very purpose of delivering an application
over the web. The idea is to have a client that is common to all users so that anybody
can access the application without having to do anything special. This client is
typically a browser of some sort that can render a HTML page on the user’s screen.
Most of the processing is done at the other end of the application, that is, at the server.
Here again there can be separation between the application and the data storage in the
database. These two layers can be on separate machines that are themselves separated
over the network.
The layering approach can bring about much greater flexibility and simplicity in
design, maintenance and usage. In a monolithic application, everything is coupled
together and in a layered application, we can change one layer without affecting the
behaviour of others. For example, the business logic at the application layer can be
changed without affecting the user interface or the database design. We can change
the database management system from one vendor’s offering to another without
changing the application code or the user interface.
There can be many kinds of web applications such as –
• Those with static text
• Content that is changed frequently
• Interactive websites that act on user input

6
• Portals that are merely gateways to different kinds of websites Web Software
Engineering
• Commercial sites that allow transactions
• Those that allow searches.
1.2.2 Development, Testing and Deployment
Although many basic processes and methodologies do not change, there are some
features of the development cycle of web applications that are different. While some
of these will be looked at in more detail later in the unit, we need to understand these
features to be able to effectively develop a web application project.
Development
The development of such an application has to take into account the fact that there is
now one more element in the whole behaviour of the application – the network. The
element of communication could be ignored in conventional software, but it plays a
pivotal role in web based projects. Different users can be using networks that are
slow or fast and everything in between. Networks are not fully reliable and
communication lines do drop or fluctuate in their speed. While network protocols will
take care of the issues of data reliability, this comes at the cost of uniform speed.
Designers of web applications need to take care of situations like race conditions, lost
connections, timeouts and all the other tiresome realities of wide area networks.

Web applications, if used over the Internet, can potentially have a very large number
of users. So we need to be careful about matters like machine configurations and
sizing. It is also frequently necessary to have a scalable architecture that can be
upgraded as application loads rise with the growing popularity of the site. And if the
site becomes really popular, this need can be very frequent indeed!
Testing
The testing of web applications has its own difficulties, caused mainly by the variable
speed with which inputs reach the server and responses reach the user over the World
Wide Web. It is hard to simulate real Internet like conditions in test environments that
are typically based on a local area network.
Testing tools do exist that allow inputs to be sent from machines located in different
parts of the world to the application. While comparatively expensive, they do allow
for realistic testing of the applications. There are other ways of testing the
applications by trying to simulate delays and other conditions of the real Internet. To
be able to obtain best, average and worst case response times, it is necessary to run
tests many times. Automated testing is important for such load, performance and
stress tests. They cannot be realistically performed manually.
Although interoperability and consistency are assumed to be the good features of
standardized browsers and databases, in practice there are several problems that can
arise because of the differing behaviour of browsers caused by–

• Different operating systems such as Linux, Windows versions or Unix systems.

• Different versions of the operating systems.
• Differences in other components such as the Java Virtual Machine.
• Differences in behaviour of the browsers themselves because of extensions or
incomplete adherence to standards.
• Bugs in certain versions of the browsers on certain operating systems.

It is often impractical to test the application on all possible combinations of browsers,

operating systems, databases and their various versions. In such cases the
combinations for which tests have been performed are sometimes indicated and the

7
Advanced Software appropriate fixes have to be made to the application as bugs are discovered and
Engineering
reported during field use.
Deployment
In most conventional application rollouts, there is often a fair degree of control
available to the developers because of the possibility of limiting access. Limited
releases to a select test group can be made so that the most obvious and common
errors and annoyances are taken care of before the regular release. But in a web
application that works over the Internet, it can be difficult to do such tests. True,
access can be limited by not publicising the URL at which the application is available,
or by having access control in some form that is known only to the select band of
users in the test group. Still, since the application is to be available publicly, there is a
conflict between the small group which gets early access and the possibility of
realistic testing. The very characteristic of a web application is having a large body of
concurrent users.
We have already mentioned the need for scalability in the hardware. This is
particularly important in terms of storage. We need to be careful that we do not
quickly run out of space, for example, in an e-mail or storage site. Besides, it might
be important to have the capability to beef up the bandwidth available to the server
that is hosting the application, lest it get swamped by user requests.
1.2.3 Usage of Web Applications
Applications hosted on the web are meant to be used by lay users who may have little
knowledge of computers. Conventional applications also have to deal with usage by
non- technical people, but there we can often organise training or help desks to take
care of any problems that may arise. That possibility is not available for a web based
application. Because, we cannot reach and train all of our target audience, even if it
were possible to identify them individually. As any developer with a little experience
knows, users can “exercise” software in ways that were never anticipated.
Normally, if a user comes across difficulties while using the application, she could be
expected to report the problem to the appropriate group in the organisation or to the
vendor responsible for maintaining and deploying the software. But in the case of an
application on the web, the user may simply give up and just not come back to the site
if she is not able to work the page, and that too in the first few seconds. Or, her
network connection might break while trying to use the site, and that could well be her
last visit. So, the tolerance level of users is exceptionally low in such applications.
Users can also be expected to want a fast response and if some operation is likely to
take more than a few seconds, it will be best to keep them informed. Feedback on the
state of a request is also necessary, as also instructions on what to do if they are
disconnected in the middle of a long operation.
An application on the web is much more likely to be internationalised as it might have
to cater to the needs of users from different parts of the world. You may be shutting
out a large number of potential visitors to your application if you restrict yourself to
any particular language. You should also expect to see little data entry and as much as
possible of features such as auto completion, drop down menus, look up tables and the
like.
1.2.4 Maintaining Web Applications
The maintenance of web applications has its own set of challenges. Frequent changes
to the presentation, or look and feel are expected. Many of the static text pages may
need updating ever so often and some of the content could be changing daily or
hourly. So the task of maintenance has to expand to take care of changing content and
this can be a major exercise in some sites. Business rules could also be volatile, with
new schemes and packages being frequently invented to entice the users. It means
that the maintainers have to take care of frequently changing the business logic with
little change to the other layers.

8
People are sensitive about sites that are perceived as not trendy enough and Web Software
Engineering
expectations are high as regards features, good looks and easily usable interfaces.
One might have to work hard at changing and upgrading these to keep up with the
latest advances. If a site is not changed for more than a few months, it will not be
looked upon as live or up to date. So, taking care of a web application is often much
more than just fixing bugs or updating the software to implement changes to business
rules. There is a fair amount of effort that has to be put in to improve usability.
1.2.5 Designing Web Applications
Since web applications are layered, we get a simplified design that can be easily
maintained and altered. However, that also produces the corresponding need to
design the different components to be generalised enough so that they can be useful to
a larger audience. Applications could be running under the control of an application
server for which the designers have to create and implement the requisite beans. For
some purposes, beans can be purchased from other software vendors or they could
have to be written from scratch for the application.
These days, some functionality in the application could be coming out of web
services, components on the web that can run with your application and that provide
defined behavior. An application could look for an available web service that can do
some needed action. Web services advertise their available functionality that needy
applications can tap. This distributed nature of the application greatly increases the
amount of reusability, but brings about problems of security and reliability.
The user interface in a web application is very important indeed and can often be the
tipping point in the success of a website. Ease of use and ergonomic considerations
are important. The application has to be able to cater to users of disparate skill levels
and in some countries may be required to provide access to people with disabilities.
All the above characteristics need to be kept in mind when planning and otherwise
managing a web based application project.
( Check Your Progress 1
1) The _________________ can bring about much greater flexibility and
simplicity in design, maintenance and usage of web applications.
2) One of the significant characteristics of a Web Application is to have a large
number of ___________ users.

1.3 ISSUES OF MANAGEMENT OF WEB BASED

PROJECTS
Like any other software application project, we need to use good software
development practices when faced with working on a web application. Otherwise the
project would not remain in control and we would face problems with timeliness,
budgets and quality. Before going on to the special issues, it would be useful to
review the general good practices that we need to follow.
1.3.1 Review of Good Software Development Practices
There is by now a wealth of literature and experience on how to manage software
projects. While two decades ago the software crisis was a big stumbling block and
failed or overdue projects were commonplace, the efforts of quality gurus have
resulted in much better techniques of management that address these problems. Many
projects still have trouble, but that is not because the techniques were not known but
because they were not followed.
There are several quality models available to organisations that can be followed, such
as the ISO 9001:2000 quality system model or the Capability Maturity Model
Integration (CMMI) of the Software Engineering Institute of the Carnegie Mellon

9
Advanced Software University, Pittsburgh, USA. Let us look now at some of the basic, common
Engineering
principles of software management practice.
Managing Requirements
It is very important in any project to have a clear understanding of the requirements
shared with the customer. Very often the developers have no notion of how the
software will be used or what would be nice for the user to have. While a
requirements document might be prepared and approved by the customer, there are
many issues that are hard to capture in any document, despite having detailed
discussion with customer. To ensure that the viewpoints of the developers and
customer do not diverge, regular communication is a must. Finer points that could not
be captured in the documentation have to be understood by the project team through
proper coordination with the customer. Here the customer could be an external party
or could be another group within the same organisation, in which case it is an internal
customer.
Even if we achieve a good understanding of the requirements, software projects are
notorious for changes. This means that we must have a good system of tracking
requirements as they change. The rest of the artifacts in the project must reflect the
changes that have occurred in the requirements.
Managing the Project
The essence of managing the project is proper planning for the project and then
executing the project according to the plan. If the project deviates from the plan, we
need to take corrective action or change the plan. We must always be proactive and
keep looking for the risks in the project, rather than react to problems after they have
arisen. We should try to anticipate what can go wrong and take action accordingly.
Here a plan needs to keep something apart from the schedule of the project.

The project plan is the basic document used to execute the project and has all the
required information about it. It should be the guiding document for the project and
hence must be kept up to date. Some of the items of information in the plan could be–
• Background information and context
• Customer and other stakeholder information
• Estimates of cost, effort and duration
• Dependencies on outside groups
• Resource requirements – equipment and people
• Methodology to be used to do the project
• How the project will be monitored.
• Schedule.
Besides the project management plan, there are various subordinate plans that need to
be made for different aspects of the project, such as,
• Configuration Management Plan
• Quality Assurance Plan that covers audits and process compliance
• Quality Control Plan that covers technical reviews and testing
• Risk Management Plan
• Training Plan
• Metrics Plan
• Defect Prevention Plan
There should be regular communication between the team members themselves to
ensure that there is a shared vision and sense of purpose, and that perceptions remain
aligned to the project goals.

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As the project is being executed, there has to be regular monitoring of the progress Web Software
Engineering
and of the different parameters of the project, such as effort, cost and quality. If any
of these parameters is not in line with what was planned, appropriate investigation,
analysis and corrective action needs to be taken. Sometimes circumstances change
such that it is no longer possible to bring back the project on track with the original
plan, whereupon the plan needs to be reviewed and revised.
Configuration Management
This is vital to retaining control of the artifacts produced by the project. Given that
changes will occur, we need to be able to track and know at all times which version of
an artifact is current and which ones are obsolete. We do not discard obsolete
versions because it may sometimes be necessary to backtrack or to branch off in
another direction from a common base.
Whenever an artifact is produced it should be reviewed so that we can have
confidence in the veracity and appropriateness of its content. After this it should be
placed in a baseline area and any further changes to it should be done only according
to formal change procedures. We have to plan for which artifacts will be so
controlled.
Access to baselined artifacts should be limited to a designated configuration
controller. Any member of the team who needs to alter a baselined artifact needs to
approach the configuration controller who will then check out the artifact and allow
the team member to make the change. Simultaneous checking out by more than one
team member is discouraged, but if done, any conflicting changes that may be made
by them need to be taken care of.
Measurements
It is important to measure our software work so that we can keep control of the
proceedings. This is the key to being able to manage the project. Without
measurements we will not be able to objectively assess the state of the progress and
other parameters of the project, and we would be reduced to relying on our intuition
and feel for where the project stands.
Software engineers have been notorious for not bothering to measure their work, or
for insisting that their work cannot be measured. It is an engineering discipline unique
in that measurements have not been given. However, in the 1990s, great progress was
made in spreading awareness and appreciation of the need for software measurements.
Still, even today, many organisations do not have a good metrics program going.
Risk Management
An important constituent of project management is managing the risks of the project.
A risk is an event that can have a deleterious impact on the project, but which may or
may not occur. Thinking of the possible risks is the first step in trying to take care of
them. While we cannot get rid of risks, we need to keep thinking of ways to reduce
their effects. Better still, we should try to take steps that will prevent the risk from
becoming a reality.
Not all risks need to be looked at. When we analyse risks, there are some that are
more probable and also have a significant adverse effect on the project. Others may
have a severe effect if they occur, but are not too likely to happen. Still others may
not be too harmful, even if they do come to pass. There can be a large number of risks
in a project, but thinking about all of them is not practical. We need to concentrate on
the most important risks and direct our energies to managing them.
Over time, the risk parameters can change. We, therefore need to keep re-looking at
our risks and alter our risk plan to take cognizance of the changed situation as the
project progresses. We should keep carrying out the actions that make the risk less
likely. Whenever a risk does occur, we should put into action our plan for reducing its
harmful effects.

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Advanced Software Thus risk management allows us to look at a project actively, rather than passively
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reacting to events after they have occurred.
1.3.2 Organisation of Web Application Teams
Web applications tend to need much more ongoing support, maintenance and
enhancement than others. After the initial application has been rolled out, comes the
stage of maintenance. This can amount to weekly or even daily releases in the first
instance while the software stabilises. This endeavour requires a team structure that is
a bit different from others. We start from the maintenance end to emphasise its
importance, and the fact that design and development are done comparatively quickly.
Sometimes the need for project management during development itself is questioned
but, as in any other project, good management is critical to success in a web
application project as well.
Webmaster
This role is not unique to web applications, but is usually otherwise referred to as the
administrator. It entails taking care of the site on a day to day basis and keeping it in
good health. It involves close interaction with the support team to ensure that
problems are resolved and the appropriate changes made. Some of her activities
include –
• Gathering user feedback, both on bugs (such as broken links) and also on
suggestions and questions from the public. These need to be passed on to the
support team who are engaged in adapting the site in tune with this information.
• Ensuring proper access control and security for the site. This could include
authentication, taking care of the machines that house the server and so on.
• Obtaining statistics and other usage metrics on the site. This could include,
among many others –
o Number of hits, distributed by IP address
o Number of registered visitors
o Frequency distribution of the different pages visited
o Bandwidth utilised for upload and download
o Number and type of errors, particularly of service denials.
• Helping to ensure that change control procedures are followed.
• Archiving old content while keeping newer content in a more prominent and
easy to find location.
Application Support Team
In conventional software projects, while maintenance is important, it may or may not
be done by the organisation that developed the project. In web applications, the
organisation that developed the site is quite likely to be given the responsibility of its
maintenance. This is because web applications tend to keep evolving and what
corresponds to the development phase in a conventional application is here quite brief
and frenetic. A large part of the evolution of the software tends to happen
subsequently, based on user feedback and continuing refinement of the concept by
those who conceived of the application. The activities here can consist of–
• Removing bugs and taking care of cosmetic irritants.
• Changing the user interface from time to time for novelty, to accommodate user
feedback and to make it more contemporary.
• Altering the business rules of the application as required.
• Introducing new features and schemes, while disabling or removing older ones.

The support team could consist of designers including graphic artists, programmers,
database specialists and testers.
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Content Development Team Web Software
Engineering
In conventional business application software, there are usually changes and
modifications required to master tables in databases, such as altering price lists,
available items and so forth. Web applications frequently require much more
ongoing, sustained effort to retain user interest because of the need to change the
content in the site. In the case of a news site, this updation can be every few minutes.
The actual news could be coming from a wire feed from some news agencies, or from
the organisation’s own sources.

Though not all sites need to be so current, it is often required to keep adding articles
and papers of interest to the user community. These stories or articles are written by a
team that has expertise in the domain concerned. A site could be serving out a wide
variety of information and other stories from different interest areas. Content
development teams could be researchers who seek out useful or interesting facts,
authors, experts in different areas, and so on. The content may be edited before being
served out.

The members of this team are usually not knowledgeable from the software point of
view, though they might be well respected in their own domains. They may be full
time members of the organisation or casual, freelance contributors. So though called a
team, some of them might really be individual providers. The content they produce is
typically in the form of a word processor file that might have images, graphs, tables
and other non-text ingredients.

Other forms of content are now quite commonplace, such as audio files, slide
presentations or video clippings of events, places or speakers. With increasing
availability of high speed network connections for even individual users, such content
is now becoming increasingly popular because of the impact it can produce.
Web Publisher
This is an important role that connects the content development team to the actual
website. The raw material created by the writers has to be converted into a form that
is suitable for serving out of a webserver. It means formatting the content according
to the requirements of a markup language such as HTML. Though tools can help
perform much of this, there still might be human effort that is needed.
In the case of automated news feeds, such publishing needs to be as tool driven as
possible. The web publisher must have a good understanding of the technical aspects
of web servers and the markup language.
1.3.3 Development and Maintenance Issues
Let us now look at some of the management issues that we will face while developing
and maintaining a web application. We have already seen that web applications tend
to evolve, and there is little distinction between what in a more conventional project
we would refer to as development or maintenance. It is hard to say when the
development is complete and maintenance starts in a web project. In practice it is a
continual cycle of delivering something and then of fixing and correcting and
enhancing it.
Configuration Management
During maintenance of a web application, because of the frequency of changes,
configuration management assumes considerable importance. The change control
process must be up to the demands placed on it of keeping control over the software
configuration inspite of the many changes that will happen. So it must not be overly
elaborate or hard to follow. That would mean it might not get followed and the
consequences will be disturbing. Once one loses track of what is happening in the
software it can become very difficult to get back. It will then become impossible to

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Advanced Software predict the effect of changes to the software and one would have to grapple with
Engineering
mysterious bugs whose cause will be hard to find.
Besides the software itself, content also needs to be subjected to configuration
management. This could include items such as information on schemes or other
service or product offerings. Lack of discipline here could mean horrors like –
• Postings on past offerings that are no longer available,
• Incorrect prices or other terms being visible to users,
• Postings of content that is still work in progress and was not ready for
publication apart from lesser embarrassments such as archival content
reappearing on the site.
A very important aspect is that of inadequately tested code finding its way into the
active configuration. It could mean that visitors to the site have to put up with
features that do not work as expected or simply crash on them. Worse, it can result in
security holes that compromise the security and integrity of the site. Sometimes, the
privacy of data of registered users could be in question. In other cases it could expose
other systems of the organisation itself to unauthorised intruders.
Since contributions to an organisation’s website can come from diverse sources and
departments, it can become difficult to establish accountability and responsibility for
the web application. In conventional business software applications it is clearly a
particular division or group in the company that is served and that would have an
interest in the software working properly. This interest is often diffused and spread
out in a web application. It cannot be the technical team or the software wing, as this
is often an outsourced vendor. In any case the ownership of the application needs to
be assumed by the business and not a technical group. While there can be many
claimants for ownership and authority, the same may not hold when it comes to
owning responsibility.
To determine who is responsible for the website, some of the relevant questions can
be –
• Who pays for the website (this can be a charge to an internal budget)?
• Who is concerned with the accuracy of the content that is published?
• Who gives the requirements to the development or maintenance team?
• Who ensures quality control checks and does the acceptance check?
It is this owner of the website who should be ensuring that proper configuration
management practices are followed. Even if this question is resolved, we have to
grapple with how exactly to do configuration management. The identification of
configuration items can be difficult. This is because there are many components to a
web application, and some items such as news content can be very short-lived. Other
content can last longer. To what extent does one look at configurations for transient
content? Perhaps just recording when it was published and when it was removed is
sufficient. For other content that may appear for days or weeks, we might have to
deal with normal, conventional changes and updates. What constitutes a configuration
unit is also not easy to define, as hyperlinks from within content can complicate the
matter.

Conventional configuration management tools are also not really suited to deal with
this kind of constant evolution. The usage of these tools is also made difficult because
many in the maintenance team, such as content developers, may not be familiar with
software, let alone the tools. Also, web application support teams may not be
geographically located in the same place and people could be working in different
places. So the tools used need to be such that they can be operated over the network.
Project Management
If configuration management has its challenges as described above, they pale into
insignificance compared to the difficulties we may have while managing the web

14
application project itself. When we look at the elements of project management the Web Software
Engineering
reasons will become apparent.
1. We have already seen that evolution and hazy, fluid requirement specifications
are the norm here. How then does one perform estimation? That presupposes a
clear knowledge of the scope and specifications.
2. More than in any other kind of software, schedules are dictated by the users.
Quite often, the software is the means to seize upon a business opportunity that
may be available for a small window in time. So the developers or maintainers
may not have much influence on the time they can get. Whatever the estimate,
the software has to be delivered by the date the user needs it.
3. Coordination and human issues can be more daunting than ever. The team may
be geographically dispersed, may come from disparate backgrounds and may
have conflicting interests or vision.
4. The question of ownership we have already seen in the section on configuration
management. Even though stakeholders may not be hard to identify, overall
accountability and responsibility could be.
5. The metrics to use to gauge success have to be identified carefully, keeping in
mind the unique characteristics of a web application.
6. The actual engineering aspects, particularly analysis, design and testing have to
be tuned to the life cycle of such a project. Agile programming methodologies
may be of help here.
7. Quality assurance is made more difficult by the frenzied pace of activity that
may induce the harried project team to jettison process driven working.
While none of these challenges permit of simple solutions, we can try to keep some
things in mind and work towards keeping the project under control by –

• Recognising that the software will follow an iterative life cycle model for
development, with each iteration being quite short. We may not be able to work
out a grand plan for the whole project as it will be at the end, simply because we
cannot predict what shape it will take eventually. So we could concentrate on
the current iteration and be clear about what we will deliver in that one. Other
items on the user wish list should be taken care of in the next delivery. Save in
exceptional circumstances, do not alter the objectives or scope of the current
iteration.
• The question of schedule is a difficult one. Managing expectations of the users
is imperative here. If what the user’s desire is clearly unattainable, we need to
negotiate and reduce the scope for the current iteration. Also with more
experience in getting a web application developed, the users will hopefully have
a better appreciation of what is possible.
• With current day groupware and other tools, we can make it simpler to work
with distributed teams. But there should be adequate attention paid to
communication among team members so that the objectives of the project are
clear. As in a conventional project, we should have team meetings regularly,
even if those meetings are done over the telephone or using network meeting
tools.
• As always, the processes to be followed in the project should be appropriate to
the situation. They should not be cumbersome or difficult to do, so that the
project team will be able to follow them. We need to remember that if the
processes are complex and are not followed, the impact on the project is much
worse, as we potentially could lose control of what is happening.
In subsequent sections we will be reviewing the strategies to follow to get a grip on
the other issues such as life cycle activities and measurements to be made. The other,
usual elements of project management such as managing risks, analysing defects and

15
Advanced Software trying to prevent them or monitoring project parameters such as cost, effort, schedule
Engineering
and quality, remain as valid as in any other software project.
( Check Your Progress 2
1) The essence of managing the project is proper ________ for the project and
then executing the project according to the plan.
2) The __________ process must be up to the demands placed on it of keeping
control over the software configuration in spite of the many changes that will
happen.

1.4 METRICS
Management of any kind is difficult, if not impractical, without measurements being
made. Those values tell us where we stand in our endeavour, whatever it may be.
Software engineers have been especially tardy in understanding the need for
measurement, preferring to rely on intuition and subjective assessment. However,
realisation does seem to have set in and many software projects do measure at least
the basic parameters like schedule, effort and defects. When it comes to cost,
practices seem to vary across organisations. Some are secretive about the costs of
projects and only senior management is privy to such information. Others place the
responsibility for the budget for the project on the shoulders of the project manager.

In web applications, these core metrics need to be measured and analysed just as in
any other software application. Schedules could be made fine grained so that we are
tracking things on small, quick milestones rather than only at the “end” of the project,
which is difficult to define here. That could mean that it may not be very meaningful
to measure them in terms of slippages (a one-day delay in a task lasting a week is
14%). One possibility could be to look at the percentage of schedules that could not
be kept.

Effort metrics can be gathered through a time sheet and we can measure the total
effort in different kinds of activities to build up our metrics database for future
guidance. However, here we need to be sure to record the actual effort and not try to
confine it to a conventional workday of 8 hours. Metrics data on effort is valuable in
building up a body of knowledge for future estimation. This data should be recorded
under time spent on analysis, design, construction, project management and so forth.
Past data is also helpful in negotiating with users for a reasonable amount of time to
perform a task

Another core attribute of a software project is its size. This should preferably be
measured in an implementation independent way, such as function points. The
International Function Point Users Group (IFPUG) has come up with guidelines for
measuring the size of a web application from the user point of view. If the
organisation has good reason to feel that this measure is not suitable, then the creation
of one’s own size measure could be considered. If a good size measure can be built,
then it can be used to estimate the effort required for future projects, provided the
productivity factor that converts the size to effort is available from data on past
projects.
The quality of the application can be measured in terms of defects that are found
during internal testing or reviews as well as external defects that are reported by
visitors who come to the site. But all defects are not equal, and we need to analyse
defect data carefully. Some attributes that can be used to classify defects for further
analysis are:
• Severity on a scale of 3 levels, such as high, medium and low. More levels up
to 5 can also be considered. The severity is in terms of impact on the usage of
the software by the user.
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• Phase in the life cycle where they were introduced, such as analysis, design or Web Software
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coding.
• Whether they are internal defects, detected by the development or testing team,
or whether they were found by the end users.
• Whether they were detected during reviews or during testing.
• Effort required to fix the defect, as this might not have any correlation to the
perceived severity of the defect.
Such an analysis would then form the basis for the formulation of a defect prevention
plan for the software project. We would strive to prevent the kind of defects that are
of high severity or those that take a lot of effort to remedy.
We can also look at other measures like –
• Percentage human resource utilisation in the project. Roles that are idle for
significant periods could be allocated to another project as well.
• Percentage of code that is reused from the organisation’s library of such
components.
• Quantum of changes to the user requirements as the project progresses. An
overly high value could indicate that more effort needs to be directed towards
scoping out the project and eliciting the requirements.
• Percentage of attrition in the project. An unusually high value for this could
point towards problems in managing the human angle.

Besides metrics to give insight into the development aspects of the project and the
general state of the team, there can be a large number of statistics and measures that
can be gathered about the usage of the website once it has been put into active use.
Some of these have been already touched upon in earlier section under the role of
Webmaster. Most of them rely on traffic analysis to draw conclusions about the users
and their interests. This can give an insight into what changes should be made to the
site or how it can be improved.

We can also look at some metrics from the point of view of maintenance. These could
be the average time taken to fix bugs of different severity levels, together with the best
and worst case times. Other measures can include –
• User satisfaction index
• Mean time between failures (bugs detected or reported)
• Number and percentage of repeat visitors.
Gathering and calculating metrics is only one part of the work involved here. The
crux of the matter is how well the knowledge of metrics is used to shape the
functionality and features of the project. The metrics should be aligned to the goals
and objectives of the project and the lower level measures should be derived from the
top level ones, so that we measure whatever is important for us and do not gather
extraneous data. From a measurement deficient situation it is quite possible to go
overboard and drown oneself in a mass of low level data that is not meaningful or
useful.

1.5 ANALYSIS

The usual principles of analysis continue to apply to a web software application as

well. So the requirements have to be, as always, elicited, represented and validated.
These are then the basis for further work in the project. Let us look at some of the
characteristics that we need to bear in mind while analysing a web application project.

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Advanced Software It is particularly important to be clear about the process owner and the stakeholders
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here. We must not end up getting wish lists and requirements from someone who, it
later turns out, is not the one authorised to provide them. While always a point of
concern, the issues of ownership of the web application accentuate the problem. From
the scope that would have been talked about while setting up the project, the detailed
system analysis would need to be done to come up with the requirements.

Besides the normal considerations of what the application has to do, we need to look
at how the user will interact with the application even more closely than in a
conventional application for the reasons we have already looked at in the beginning of
this unit. The user interface has to be simple to use, visually appealing and forgiving
of a lay visitor who may not be familiar with computers or software. The actual
functionality of the application is something that has to be ensured the same way as it
would be for any other software, being the very reason for going to all the trouble.
Where things are different is in the importance of content to a web application. We
have to work out what will be shown to the user, such as a product brochure, an
offering for a tour package or anything else. This has to be placed before the user in a
manner that will be eye catching but not garish, and the user has to be able to obtain
some benefit from the offering without having to do anything elaborate.

More than in conventional applications, it is hard to distinguish entirely between

analysis and design in a web application. The kind of actual content that has to be
shown needs to be studied to decide on the best way of displaying it on the site.
Whether the user will like to show it as text, graphics, audio or video is something that
will depend on the resources available for hosting the site as well as on considerations
that have to do with the resources available with the group of people that can be
expected to visit the site. It is here that the study of the target audience becomes
crucial. This should be done on considerations that have to do with –

• Geographical region,
• Language, beliefs and culture,
• Social strata,
• Age group and gender.
and other similar characteristics. All of these demand that we change our design to
appeal to our typical visitor.

1.6 DESIGN AND CONSTRUCTION

In designing the functional aspects of a web application, we work much as we would
for a conventional application. Because of the compressed time scales and volatility,
we should consciously look to reusing as many things as possible. Reuse is always
desirable but becomes imperative in the case of a web application. While code and
object libraries come first to mind when we think of reuse, there are elements that can
be reused for the design as well. We should, for instance, be seeking out any available
design patterns that can be reused.

The advent of application servers and other component-based technologies has

facilitated the task. The application server gives the framework under which the
application can run and takes care of many mundane details that would otherwise be
the burden of the programmer. Security and persistence are two such tasks. The
functionality of the application is provided by stringing together beans, many of which
may have been already written or can be purchased from third parties. There are also
other architectural models from other vendors to help write such applications.

Where we have to lay great emphasis is on the user interface. There are several
aspects to creating a good one, some of which are:

18
1. Visual appeal and aesthetics: This is the domain of a graphic artist. Things Web Software
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such as cute sound effects, blinking and moving images that can appear
interesting or attractive for the first couple of times can irritate after a while. So
a pleasant, clean visual design is perhaps a safe bet to hold continuing interest
on repeat visits. However, if there is ever a choice between graphical appeal
and functionality, we must plumb for functionality every time.
2. Ease of entry of data: Given the fact that most users may be unfamiliar with
computers or software, data entry should be as simple as can be made. Actual
entry using the keyboard should be kept to the minimum. Allow for using the
mouse for selection from lists. It should be easy to ask for information of the
application.
3. Ease of obtaining the application’s response: Whenever we query the
application, the results should be easy to see and interpret. If the processing is
going to take a while, give visual feedback to the user on how long she can
expect to wait. At no point should a user feel lost, not knowing where s/he is in
the site or what she should do next. Context sensitive help should be available
throughout the site.
4. Intuitive, easy navigation around the site: As a visitor navigates around the
site, there should be some aids to helping her find her bearings. Things like a
site map and your location on it are useful. It should be possible to come back
to a reference point like the home page in a single click from anywhere deep in
the site. It is our application that should provide all navigation facilities and we
must not expect the user to use browser buttons to go around.
5. Robust and forgiving of errors: If there is any erroneous input, the
consequences should not be too inconvenient. We should expect a discreet and
graceful error message, not a disconnection from the server. It should not
happen that we land up in some error page that does not give us any explanation
of what went wrong.
Website users would not like to have to scroll and so we must try to see that this is not
required for any screen resolution. A horizontal scroll is much more irritating than a
vertical scroll to most users.

1.7 REVIEWS AND TESTING

In this section we will look at some of the considerations for reviewing testing web
applications. The content of a website is the item of interest to the visitor and so we
must take care to review all content to make sure that there are no errors of fact or
language therein. Besides, the design of the site should be reviewed to catch errors
like difficulties in navigation or data entry.

It may not be very useful to merely check out the components of a website on a
standalone basis as part of unit testing. While in a conventional application a program
is the smallest unit that we test, in web applications it is more likely to be a single web
page. We should check out the content, the navigation and the links to other pages as
part of testing out a page. There should not be any broken links that leave the user
bemused. If there is some functionality being provided by that page, that part should
work correctly. This part of the software is close to a conventional application and the
actual processing that happens can be unit tested as usual. Where the processing is
done by using bought out components, it may not be necessary to unit test those
components. We would then only have to concentrate on checking out the full
functionality.

Once all the pages of the web application are ready we can perform integration
testing. We check out how the pages work together. Whenever an error is caught and
fixed we should repeat the tests to ensure that solving a problem has not caused

19
Advanced Software another problem elsewhere. It is possible that individual pages work well but not
Engineering
together.

Unlike a conventional application, here we do not have much control (except our
instructions to users) on all parts of the working system. This is because we do not
know what browser, what version of it and what operating system the user will be
working with. While it may not be practical to test out with all possible combinations,
we should ensure that the application works with most sets of browsers and operating
systems. We should also see that the software works at different screen resolutions.
The network bandwidth expected should also be clearly decided and we should test
things out at all network speeds up to the lowest.

The actual implementation of the application has to be done carefully. In the

deployment environment, the configuration has to be checked out to be in tune with
what the application was designed and constructed for. Thereafter we may release the
software to a limited test group of users to gather their feedback before making it
public.

( Check Your Progress 3

1) The _____________ gives the framework under which the application can run
and takes care of many mundane details that would otherwise be the burden of
the programmer.

2) In the _______________ environment, the configuration has to be checked out

to be in tune with what the application was designed and constructed for.

1.8 SUMMARY

This unit has been a very brief introduction to different aspects of engineering web
software applications. While a lot more could have been written about each topic, and
other topics could have been added here, we have been able to concentrate on only a
few important points here that are with in the scope.

• Web applications have many points in common with conventional software

applications, but have their own unique characteristics.
• There are differences in the ways web applications are developed, deployed,
tested and maintained.

o Web applications often do not have a clear dividing line between

development and maintenance and usually continue to evolve.

o They have to be developed and put into use quickly and so try to make
use of reusable components as much as possible.

o The user interface is very important because they are used by lay visitors.

o Testing them can be difficult

• Following good management practices like project management and

configuration management of web applications is not straightforward because of
their characteristics.

• We need to think through the metrics we will use to evaluate project progress
and product quality of web applications.

20
 Web Software
1.9 SOLUTIONS/ANSWERS Engineering

Check Your Progress 1

1) Layering approach
2) Concurrent

Check Your Progress 2

1) Planning
2) Change control

Check Your Progress 3

1) Application server
2) Deployment

1.10 FURTHER READING

Software Engineering – A Practitioner’s Approach, Roger S. Pressman; McGraw-Hill
International Edition.
Reference Websites

• http://sei.cmu.edu/cmmi
• http://standards.ieee.org

21
Advanced Software
Engineering UNIT 2 MOBILE SOFTWARE
ENGINEERING
Structure Page Nos.
2.0 Introduction 22
2.1 Objectives 22
2.2 Introduction to GSM 22
2.3 Wireless Application Development using J2ME 23
2.4 Introduction to Java Device Test Suite 28
2.5 Summary 28
2.6 Solutions/Answers 29
2.7 Further Readings 29
2.8 Glossary 29

2.0 INTRODUCTION
This unit introduces learner to the subject of development of mobile applications.
With the increased usage of mobile devices across the world, more and more
applications are being targeted at them. If an application that is developed for
computers can also run on the mobile devices, then the entire paradigm of application
usage changes as it enables the user to run application from wherever he is.

There were different standards on which the mobile networks are based. One of the
popular standard is GSM. In this unit, we introduce the GSM architecture. There were
a number of environments under which mobile applications can be developed. One of
the popular environments is Java. We introduce J2ME (Java 2 Micro Edition) in this
unit in conjunction with wireless application development with it. Any application
should be tested before being put to full-fledged use. In this unit, Java Device Test
Suite is introduced with the help of which wireless applications can be tested.

2.1 OBJECTIVES
After going through this unit, you should be able to:
• know the GSM architecture;
• know about wireless application development using J2ME, and
• know about Java Device Test Suite.

2.2 INTRODUCTION TO GSM

Mobile devices are used by a number of people across many countries. In this unit,
mobile devices refer to mobile phones. Every country is having a set of standards on
which the mobile devices in their country are based upon. GSM is one of the popular
architectures on which mobile devices are based on. GSM stands for Global System
for Mobile Communications.

GSM is a digital wireless network standard. All mobile devices that are based on
GSM standard across the world will have similar capabilities.
The following are some of the features of GSM:
• If a mobile device is based on GSM, then it can be used in all those countries
where this particular standard is prevailing.
22
• Almost all the services that are existent in a wireline network are provided by Mobile Software
GSM to all the users of mobile devices which are based on it. Engineering

• Though the quality of voice telephony is not excellent, it is not inferior to the
systems that are analog based.
• It also provides good security as there is an option to encrypt the information
that is being exchanged using this standard.
• There is no need for significant modification of wireline networks due to the
establishment of networks based on GSM standard.
Architecture of GSM
There are three different parts in a mobile device. They are SIM card, Mobile
equipment and Terminal equipment. SIM stands for Subscriber Identity Module. A
mobile device can be loaded by any SIM. The number of the mobile device is
associated with the SIM. The size of a SIM is similar to that of a smart card. Every
SIM is also having a PIN (Personal Identity Number) associated with it. After loading
the SIM into the mobile device, the user is asked to enter the PIN. Only on entering
the correct PIN, the user will be able to start using the services offered by the mobile
operator. Initially, PIN is loaded by the operator. The PIN can be changed by the user.
If the user is unable to enter the SIM correctly for the first time, then s/he is given an
opportunity to re-enter it for a fixed number of times. In case, s/he is not able to enter
it correctly and exhausted all the tries, then the PIN is blocked. So, that particular SIM
cannot be used unless the network operator activates it. The SIM can be unblocked
only on entering the correct PUK (PIN Unblocking Key). Information related to
subscriber, PIN and PUK codes are present in SIM.
The architecture of GSM is composed of Mobile devices, Base Station Systems
(BSS), Mobile Switching Center (MSC) etc. The communication between Mobile
device and BSS is through radio interface. BSS communicates with MSC by
connecting to Network and Switching Subsystem (NSS). An MSC is a telephone
exchange that is specifically configured for mobile applications. Mobile devices and
Public Switched Telephone Network (PSTN) interface through Base stations. BSS
consists of a Base Transceiver Station (BTS) and Base Station Controller (BSC).
Equipment related to transmission, reception and signalling is part of BTS and this
equipment is used by it to contact Mobile devices. BSC deals with the allocation of
radio channel and its release apart from hand off management. Using ISDN protocols,
BSC communicates with BTS.
Apart from GSM, there are other standards such as CDMA etc.

2.3 WIRELESS APPLICATION DEVELOPMENT

USING J2ME
Java supports mobile application development using its J2ME. J2ME stands for Java 2
Platform, Micro Edition. J2ME provides an environment under which application
development can be done for mobile phone, personal digital assistants and other
embedded devices. As like any other Java platform, J2ME includes API’s
(Application Programming Interface) and Java Virtual Machines. It includes a range
of user interfaces, provides security and supports a large number of network protocols.
J2ME also supports the concept of write once, run any where concept. Initially, an
application can be developed using J2ME targeting a specific type of devices. Then,
the same application can be used for different types of devices. Also, it is possible to
use the native capabilities of these devices. J2ME is one of the popular platforms that
is being used across the world for a number of mobile devices, embedded devices etc.
There is a huge market for applications that target wireless world. Some of the

23
Advanced Software wireless applications are Games, Applications that access databases, Location based
Engineering services etc.

The architecture of J2ME consists of a number of components that can be used to

construct a suitable Java Runtime Environment (JRE) for a set of mobile devices.
When right components are selected, it will lead to a good memory, processing
strength and I/O capabilities for the set of devices for which JRE is being constructed.
Currently, two configurations are supported by J2ME. They are Connected Limited
Device Configuration (CLDC) and Connected Device Configuration (CDC). Each
configuration consists of a virtual machine and a set of class libraries. Each
configuration provides functionality of a particular level to the set of devices that have
similar features. One of the features is network connectivity. To provide a full set of
functionalities, a profile and an additional set of APIs should be added to the
configuration. These additional APIs will enable the usage of native properties of
devices as well as define suitable user interface. Each profile will support a smaller set
of devices among the devices that are supported by the chosen configuration.
In the case of J2ME, often CLDC is combined with MIDP. MIDP stands for Mobile
Information Device Profile. This combination provides a Java based environment for
cell phones in which applications can be developed. It is always possible to add
optional packages to the configuration that was already selected to support an
additional set of services. An optional package consists of a set of standard APIs that
help us to use latest technologies such as connecting to databases from cell phones,
blue tooth, multimedia etc. It is never mandatory to use optional packages. In fact, it is
to the developer to select those optional packages which provide the additional
functionality as per his desire.
CDC is the larger of the two configurations supported by J2ME. CLDC is designed
for devices that have less memory, slow processor and unstable network connections.
CLDC is suitable for cell phones. Such devices have a memory that ranges from
128KB to 512KB. Java has to be implemented within this memory. CDC is designed
for devices that have larger memory, faster processors and a significant network
bandwidth. TV set top boxes, high range PDAs (Personal Digital Assistant) are
examples of the devices that are suitable for CDC. CDC consists of a JVM (Java
Virtual Machine) and Java software that includes a significant portion of J2SE (Java 2
Standard Edition) platform. Usually, devices that are suitable CDC at least possess
2MB of memory in which Java software can be loaded.

MIDP is designed for cell phones and other lower level PDAs. User interface, network
connectivity, local data storage and application management are offered by MIDP for
applications that are based on mobile devices. The combination of MIDP and CLDC
provides a full-fledged Java runtime environment for the mobile devices. The
environment provided by their combination will add to the features of the mobile
devices. This will lead to a better power consumption and efficiency in memory
utilisation. The lowest level profile for CDC is known as Foundation Profile (FP). FP
provides embedded devices which does not have a user interface with network
capability. There are two more profiles, namely, Personal Basis Profile (PBP) and
Personal Profile (PP). FP can be combined with these profiles to provide GUI
(Graphical User Interface) for the devices that require it. All the profiles of CDC are
in a layered manner. This will facilitate adding as well as removing profiles as per the
need of features.
PP is useful for all the devices that require a GUI, Internet support etc. Usually,
devices such as higher level PDAs, Communicators etc. need such features. Java
AWT (Abstract Window Toolkit) is contained in this profile. It also offers web
fidelity, applets etc. PBP is a subset of PP. PBP supports application environment to
those devices in the network that support at least a basic graphical representation. PP
as well as PBP are layered to the top of CDC and FP.

24
There are several reasons for the usage of Java technology for wireless application Mobile Software
development. Some of them are given below: Engineering

• Java platform is secure. It is safe. It always works within the boundaries of Java
Virtual Machine. Hence, if something goes wrong, then only JVM is corrupted.
The device is never damaged.

• Automatic garbage collection is provided by Java. In the absence of automatic

garbage collection, it is to the developer to search for the memory leaks.

• Java offers exception handling mechanism. Such a mechanism facilitates the

creation of robust applications.

• Java is portable. Suppose that you develop an application using MIDP. This
application can be executed on any mobile device that implements MIDP
specification. Due to the feature of portability, it is possible to move
applications to specific devices over the air.
You can use J2ME wireless toolkit for development of wireless applications using
J2ME. It is possible to set up a development environment by using the following
software:
• J2SE (Java 2 Standard Edition) SDK (Software Development Kit) of v1.4.2 or
upwards.

• J2ME (Java 2 Micro Edition) Wireless toolkit. Using this toolkit, MIDlets can
be developed.

• Any Text editor.

MIDlets are programs that use the Mobile Information Device Profile (MIDP).
The first step is to install J2SE SDK. J2ME wireless tool kit runs on the Java platform
provided by J2SE. J2SE needs to be installed because it consists of Java compiler as
well as other requisite software which is used by J2ME wireless tool kit to build
programs.

The second step is to install J2ME wireless toolkit. It is possible to develop MIDP
applications using J2ME wireless toolkit. The J2ME wireless toolkit uses the concept
of projects rather than files. Once J2ME wireless toolkit is installed and run, we can
start creating projects. At the end of the creation of the project, you have on MIDP
suite. Once the project is created, its properties can be changed. Also, the project can
be build and executed in the device emulator. Let us create a new project. Let the
title of the project be project1. Along with the title of the project, MIDlet class name
should also be given. Let it be projectlet1.
Once these names are confirmed, the process of creating the project project1
commences. As the result of creation, a directory titled project1 will be created in
which the following subdirectories will be present:
• bin
• lib
• res
• src

A compiled MIDlet suite (a .jar file) and the MIDlet suite descriptor (a .jad file) are
created in the bin directory. Extra JAR that are to be used in the project may be placed
in the lib directory. Any resource files such as images, text files etc. may be placed in
the RES directory. The source code created by you will be in SRC directory. Apart
from the above mentioned subdirectories, the following subdirectories are also
created:
25
Advanced Software • tmpclasses
Engineering
• tmplib

But, these subdirectories are not used by the developer explicitly. They are basically
used internally.
The details of code with which MIDlets can be developed is a larger topic and
references may be studied for it.
Once the MIDlet projectlet1 is developed, it should be saved as projectlet1.java file in
the SRC directory. The following is the exact location of this file:
• D:\WTK22\apps\project1\src\projectlet1.java
Now, build the project. After successful build, run it. Upon running, a mobile phone
emulator will pop up. In the emulator, the title of the project will be displayed along
with a button labelled Launch. On clicking it, the MIDlet developed will be executed
and the result is displayed on the screen. There is a button labelled Exit at the bottom
of the display on which the MIDlet is executed. If the Exit button is clicked, then, we
exit the MIDlet that is executed. Now, there are two ways to exit the emulator. Either
the emulator window can be closed or ESC key can be pressed.
There are a number of emulators provided by J2ME wireless toolkit. One of them can
be selected from the KT (ToolKit) tool bar. After selection, we need to execute the
project again.

When the project is build, the toolkit will compile all the .java files in the src
directory. The compilation is performed in the MIDP environment. There were
different APIs in the MIDP and J2SE environment. When the project is being
compiled in the MIDP environment, then the APIs from MIDP should be considered
for the classes that are used in MIDlets. The corresponding APIs in J2SE are not used.
All MIDP classes are verified in two phases before they are loaded and executed. At
build time, the first verification is done by J2ME wireless toolkit. When classes are
loaded, the second verification is done by device’s runtime system. Finally, all
MIDlets are packaged into MIDlet suites. These suites are distributed to actual
devices.
Along with the J2ME wireless toolkit, information about the following is also
provided:
• Application development cycle
• Attributes of MIDlet
• Files in the installed directories
• Device types
• Portability
• Guidelines on the process of configuring an emulator
• Usage of J2ME wireless toolkit.

Until now, we focused on the development of MIDlet. It is possible to do a bit of extra

work and make these MIDlets work across networks. For this to happen, we may need
to develop servlets to whom MIDlets can establish network connections.
For developing servlets, we need server. Tomcat is the server that can be used for this
purpose. There are a number of servers available and every server is having its own
advantages and disadvantages.
The first step is to install and run Tomcat. The latest version can be downloaded from
the website of Apache Jakarta Project. It comes as a ZIP archive. After downloading,
it can be installed into any directory. Tomcat is written in Java. Tomcat needs the
location of J2SE to run. Hence, the location of J2SE should be set in the
26
JAVA_HOME environment variable. Once, all these steps are performed, then, open Mobile Software
the command window. Change to the bin directory of Tomcat. Type startup at the Engineering
prompt. That’s it. Tomcat starts running. Don’t worry about the things that are
displayed on the screen once you start it.

It is possible to check whether Tomcat is really running or not. For that, just open the
browser window. Try to open http://localhost:8080/. If a default page from Tomcat
with links to servlet and JSP examples is displayed, then, it means that the Tomcat is
running. To shutdown the Tomcat, open the command window. Change to bin
directory of Tomcat and then type the command shutdown. That’s it. Tomcat starts
shutting down.

Now, suppose that a servlet called counter is developed. The name of the file will be
counter.java. It should be saved to the root directory of Tomcat. Once it is saved to the
root directory, it can be compiled. To compile servlets, there is need for servlet API.
This should be added to the CLASSPATH before compiling servlets. The servlet API
is present in common/lib/servlet.jar under the Tomcat directory. Now, the counter.java
servlet can be compiled using javac as follows:
D:\>javac counter.java
Let us place this servlet in a web application. The servlet can be saved to a directory
in webapps directory of Tomcat. Let this directory be abcd. Tomcat will know about
the new web application through its configuration files. The necessary changes to the
configuration files needs to be done by the developer. This can be done by opening
the server.xml file from conf directory and adding a context entry.
The reason for performing all these steps is to handle the incoming http requests. If
the request begins with /abcd, then the request will be sent to the web application that
is located at webapps/abcd. The most important file in any web application is
web.xml. It is always stored in WEB-INF directory. This is the time when we start
thinking about making the servlet counter.java accessible to the entire world. Suppose
that counter.java is placed in a directory called count.
Now, the following is the full path to the servlet:
http://localhost:8080/abcd/counts
Now, necessary changes are to be done to web.xml file so that Tomcat will know that
counter servlet should be mapped to abcd/counts.
As we have seen, both servlets and MIDlets can connect to the world via http. Hence,
connecting MIDlet to servlet is not a complicated issue.
The following are different steps in the process of connecting MIDlet to a servlet:
• Start Ktoolbar. This is part of J2ME wireless toolkit.
• Open the project1.
• Write the code for the MIDlet (let it be countmidlet.java) that connects to
counter servlet.
• The screen of countmidlet.java (after executing it) consists of two commands
namely Exit and Connect. Clicking on Connect will lead to the invocation of
connect( ) method that will establish a network connection. It will also transport
the result.
• The countmidlet.java should be saved to apps/project1/src directory under
J2ME wireless toolkit directory.
• Now, J2ME wireless toolkit should know that a new MIDlet is added to it. This
can be done by going to SettingsÆ MIDletsÆAdd. Enter countmidlet for both
the MIDlet name and class name. Click on OK.
• Go to SettingsÆ User Defined. Add the property name as countmidlet.URL.
This URL will invoke counter servlet.
27
Advanced Software
Engineering ) Check Your Progress 1
1) J2ME never needs J2SE. True False
2) Tomcat can be used for developing ___________.
3) MIDP stands for ____________.

2.4 INTRODUCTION TO JAVA DEVICE TEST

SUITE
Using Java Device Test Suite (JDTS), it is possible to test the J2ME applications. The
implementations of CLDC and MIDP can be evaluated using this test suite. They can
also be validated and verified.
The following are different types of tests can be conducted using JDTS:
• Functional tests
• Stress tests
• Performance tests
• Security tests.

During functional testing, the application is tested whether it behaves as intended or

not. It’s behaviour with both internal and external components is checked. During
stress tests, the application will be run under the upper limits of the memory and the
processing power. During performance tests, response time etc. are evaluated. Under
security tests, the MIDlets are checked for their security model which also includes
access permissions.
It is possible to include additional test suites to JDTS depending on the requirement.
This will enable the developer to execute a select set of test cases. It is also possible to
automate the entire testing process. But, in this case, test results does not include the
cases where problems may arise due to interaction with application. In JDTS, there is
a Test Console as well as a Test Manager which help developers to test their J2ME
applications.
The following are some of the features of JDTS:
• More than one test suite can be executed at once.
• Test Manager can accept connections from multiple test consoles concurrently.
Each test console might be testing several devices with the same configuration.
• Test reports are generated in HTML format.

) Check Your Progress 2

1) Using Java Device Test Suite, _________ applications can be tested.
2) Only one test suite can be executed at a time in JDTS. True False

2.5 SUMMARY
The most basic issue that governs mobile devices is the standard on which they are
based on. GSM, CDMA etc. are some of such standards. In this unit, GSM is
introduced. Its architecture is also discussed. One of the most popular environments
under which wireless applications can be developed is Java. J2ME is the platform
under which wireless applications can be developed. The entire process of wireless
application development using J2ME is discussed in this unit. Finally, Java Device
28
Test Suite, which is used to test wireless applications developed using Java is Mobile Software
discussed. Different types of tests that can be conducted using are also explained. Engineering

2.6 SOLUTIONS/ANSWERS
Check Your Progress 1
1) False
2) Servlets
3) Mobile Information Device Profile.

Check Your Progress 2

1) J2ME
2) False.

2.7 FURTHER READINGS

1) Programming Wireless Devices with the Java 2 Platform, Micro Edition, 2nd
Edition, Riggs, Roger/ Taivalsaari, Antero/ Van Peursem, Jim/ Huopaniemi,
Jyri/ Patel, Mark/ Uotila, Aleksi; Addison Wesley.
2) Wireless and Mobile Network Architectures, Yi-Bing Lin and Imrich Chlamtac;
Wiley
Reference Websites

• http://java.sun.com

• http://www.rspa.com

2.8 GLOSSARY
• API stands for Application Programming Interface. It is a set of classes that can
be used in application.

• CDMA stands for Code-Division Multiple Access. It is one of the cellular

technologies. There are 3 CDMA standards, namely CDMA One, CDMA2000
and W-CDMA.

• CDC stands for Connected Device Configuration. It is a specification for J2ME

configuration.

• CLDC stands for Connected Limited Device Configuration. It is a specification

for J2ME configuration.

• CVM stands for Compact Virtual Machine (CVM). It is used by CDC and is an
optimised Java Virtual Machine (JVM).

• J2ME stands for Java 2 Micro Edition. It is a group of specifications and

technologies related to Java on small devices.

• MIDP stands for Mobile Information Device Profile. It is a specification for

J2ME.

29
Advanced Software • MIDlet is an application written for MIDP. They are derived form
Engineering javax.microedition.midlet.MIDlet class.

• MSC stands for Mobile Switching Center. It is a part of cellular phone network
which coordinates and switches calls in a given cell.

• Optional package is a set of J2ME APIs which provide specific functions such
as database access etc.

30
Mobile Software
Engineering

31
 Case Tools
UNIT 3 CASE TOOLS
Structure Page Nos.
3.0 Introduction 31
3.1 Objectives 31
3.2 What are CASE Tools? 31
3.2.1 Categories of CASE Tools
3.2.2 Need of CASE Tools
3.2.3 Factors that affect deployment of CASE Tools
in an organisation
3.2.4 Characteristics of a successful CASE Tool
3.3 CASE Software Development Environment 35
3.4 CASE Tools and Requirement Engineering 36
3.5 CASE Tools and Design and Implementation 39
3.6 Software Testing 42
3.7 Software Quality and CASE Tools 43
3.8 Software Configuration Management 44
3.9 Software Project Management and CASE Tools 45
3.10 Summary 46
3.11 Solutions/Answers 47
3.12 Further Readings 48

3.0 INTRODUCTION
Software Engineering is broadly associated with the development of quality software
with increasing use of software preparation standards and guidelines. Software is the
single most expensive item in a computer system as the cost of software during the
life time of a machine is equivalent to more than 95% of the total cost (including
hardware). Software Engineering requires a lot of data collection and information
generation. Since the computer itself is a very useful device as the information
processor, it may be a good idea to automate software engineering tasks. Computer
Aided Software Engineering (CASE) tools instill many software engineering tasks
with the help of information created using computer. CASE tools support software
engineering tasks and are available for different tasks of the Software Development
Life Cycle (SDLC). You have been introduced to CASE tools in Unit 10 of
MCS-014. This unit covers various aspects of these CASE tools and their
functionality for various phases of software development.

3.1 OBJECTIVES
After going through this unit, you should be able to:
• define different kinds of CASE tools and the needs of the CASE tools;
• describe the features of analysis, design, tools use in Software Engineering; and
• identify software configuration management, and project management tool.

3.2 WHAT ARE CASE TOOLS?

Computer Aided Software Engineering (CASE) tools are gradually becoming popular
for the development of software as they are improving in the capabilities and
functionalities and are proving to be beneficial for the development of quality
software. But, what are the CASE tools? And how do they support the process of
development of software?
CASE tools are the software engineering tools that permit collaborative software
development and maintenance. CASE tools support almost all the phases of the

31
Advanced Software software development life cycle such as analysis, design, etc., including umbrella
Engineering
activities such as project management, configuration management etc. The CASE
tools in general, support standard software development methods such as Jackson
Structure programming or structured system analysis and design method. The CASE
tools follow a typical process for the development of the system, for example, for
developing data base application, CASE tools may support the following development
steps:
• Creation of data flow and entity models
• Establishing a relationship between requirements and models
• Development of top-level design
• Development of functional and process description
• Development of test cases.

The CASE tools on the basis of the above specifications can help in automatically
generating data base tables, forms and reports, and user documentation.
Thus, the CASE tools –
• support contemporary development of software systems, they may improve the
quality of the software
• help in automating the software development life cycles by use of certain
standard methods
• create an organsiation wide environment that minimizes repetitive work
• help developers to concentrate more on top level and more creative problem-
solving tasks
• support and improve the quality of documentation (Completeness and non-
ambiguity), testing process (provides automated checking), project management
and software maintenance.
Most of the CASE tools include one or more of the following types of tools:
• Analysis tools
• Repository to store all diagrams, forms, models and report definitions etc.
• Diagramming tools
• Screen and report generators
• Code generators
• Documentation generators
• Reverse Engineering tools (that take source code as input and produce graphical
and textual representations of program design-level information)
• Re-engineering tools (that take source code as the input analyse it and
interactively alters an existing system to improve quality and/or performance).
Some necessary features that must be supported by CASE tools in addition to the
above are:

• It should have Security of information. The information may be visible/

changeable by authorised users only.
• Version Control for various products
• A utility to Import/Export information from various external resources in a
compatible fashion
• The process of Backup and Recovery as it contains very precious data.
32
Figure 3.1 shows an environment having CASE. Case Tools

Coding support Project

Management
Functions

Back up and
Recovery Prototyping
Tools
The
repository
Documentation tools Configuration
management

Analysis and Design

Modelling Tools

Export / Import Information Security Query and report generator

Figure 3.1: CASE Tools

3.2.1 Categories of CASE Tools

On the basis of their activities, sometimes CASE tools are classified into the following
categories:
1. Upper CASE tools
2. Lower CASE tools
3. Integrated CASE tools.
Upper CASE: Upper CASE tools mainly focus on the analysis and design phases of
software development. They include tools for analysis modeling, reports and forms
generation.
Lower CASE: Lower CASE tools support implementation of system development.
They include tools for coding, configuration management, etc.
Integrated CASE Tools: Integrated CASE tools help in providing linkages between
the lower and upper CASE tools. Thus creating a cohesive environment for software
development where programming by lower CASE tools may automatically be
generated for the design that has been developed in an upper CASE tool.
Figure 3.2 shows the positioning of CASE tools in a Software Application
development.
User Needs
Upper CASE
Tool

Analysis and
Integrated
Design Models
Screen designer CASE tool
Report designer
Code designer
Program editor
(Lower CASE tools)
Programmer’s
Source code
Tool kits
Compliers
Linkers
Interpreters
Debuggers
Machine
Instructions

Figure 3.2: The CASE tools and Application Development

33
Advanced Software 3.2.2 Need of CASE Tools
Engineering
The software development process is expensive and as the projects become more
complex in nature, the project implementations become more demanding and
expensive. The CASE tools provide the integrated homogenous environment for the
development of complex projects. They allow creating a shared repository of
information that can be utilised to minimise the software development time. The
CASE tools also provide the environment for monitoring and controlling projects such
that team leaders are able to manage the complex projects. Specifically, the CASE
tools are normally deployed to –
• Reduce the cost as they automate many repetitive manual tasks.
• Reduce development time of the project as they support standardisation and
avoid repetition and reuse.
• Develop better quality complex projects as they provide greater consistency and
coordination.
• Create good quality documentation
• Create systems that are maintainable because of proper control of configuration
item that support traceability requirements.
But please note that CASE tools cannot do the following:

• Automatic development of functionally relevant system

• Force system analysts to follow a prescribed methodology
• Change the system analysis and design process.
There are certain disadvantages of CASE tools. These are:

• Complex functionality
• Many project management problems are not amenable to automation. Hence,
CASE tools cannot be used in such cases.

3.2.3 Factors that affect deployment of CASE Tools in an organisation

A successful CASE implementation requires the following considerations in an

organisation:
1. Training all the users in typical CASE environment that is being deployed, also
giving benefits of CASE tools.
2. Compulsory use of CASE initially by the developers.
3. Closeness of CASE tools methodology to the Software Development Life Cycle
4. Compatibility of CASE tools with other development platforms that are being
used in an organisation.
5. Timely support of vendor with respect to various issues relating to CASE tools:
• Low cost support.
• Easy to use and learn CASE tools having low complexity and online help.
• Good graphic support and multiple users support.
6. Reverse Engineering support by the CASE tools: It is important that a CASE
tool supports complicated nature of reverse engineering.

3.2.4 Characteristics of a successful CASE Tools

A CASE tool must have the following characteristics in order to be used efficiently:
• A standard methodology: A CASE tool must support a standard software
development methodology and standard modeling techniques. In the present
scenario most of the CASE tools are moving towards UML.
34
• Flexibility: Flexibility in use of editors and other tools. The CASE tool must Case Tools
offer flexibility and the choice for the user of editors’ development
environments.
• Strong Integration: The CASE tools should be integrated to support all the
stages. This implies that if a change is made at any stage, for example, in the
model, it should get reflected in the code documentation and all related design
and other documents, thus providing a cohesive environment for software
development.
• Integration with testing software: The CASE tools must provide interfaces for
automatic testing tools that take care of regression and other kinds of testing
software under the changing requirements.
• Support for reverse engineering: A CASE tools must be able to generate
complex models from already generated code.
• On-line help: The CASE tools provide an online tutorial.
Now let us discuss some of the important characteristics for various types of CASE
tools in the subsequent sections.

) Check Your Progress 1

1) What is the need of CASE tools?
………………………………………………………………………………..
………………………………………………………………………………..
…………………………………………………………………………………
2) What are the important characteristics of CASE tools?
………………………………………………………………………………..
………………………………………………………………………………..
…………………………………………………………………………………

3.3 CASE SOFTWARE DEVELOPMENT

ENVIRONMENT
CASE tools support extensive activities during the software development process.
Some of the functional features that are provided by CASE tools for the software
development process are:
1. Creating software requirements specifications
2. Creation of design specifications
3. Creation of cross references.
4. Verifying/Analysing the relationship between requirement and design
5. Performing project and configuration management
6. Building system prototypes
7. Containing code and accompanying documents.
8. Validation and verification, interfacing with external environment.

Some of the major features that should be supported by CASE development

environment are:
• a strong visual support
• prediction and reporting of errors
• generation of content repository
• support for structured methodology
• integration of various life cycle stages
• consistent information transfer across SDLC stages
• automating coding/prototype generation.

35
Advanced Software Present CASE tools support Unified Model Language (UML).
Engineering
We will elaborate on the features of CASE tools for various stages of software
development process in coming sub-sections.
CASE and Web Engineering

CASE Tools are also very useful in the design, development and implementation of
web site development.
Web Engineering requires tools in many categories. They are:
• Site content management tools
• Site version control tools
• Server management tool
• Site optimisation tools
• Web authoring and deployment tools
• Site testing tools that include load and performance testing
• Link checkers
• Program checkers
• Web security test tools.
A detailed discussion on these tools is beyond the scope of this unit. However, various
stages of development of a web project also follows the normal SDLC. These are
discussed in the subsequent sections.

3.4 CASE TOOLS AND REQUIREMENT

ENGINEERING
Let us first answer the question:
Which is the most Common Source of Risk during the process of software
development?

One of the major risk factors that affect project schedule, budget and quality can be
defined as the ability to successfully elicit requirements to get a solution.

Statistically it has been seen that about 80% of rework in projects is due to
requirement defects.
How can a CASE tools help in effective Requirements Engineering (RE)
A good and effective requirements engineering tool needs to incorporate the best
practices of requirements definition and management.

The requirements Engineering approach should be highly iterative with the goal of
establishing managed and effective communication and collaboration.

Thus, a CASE tool must have the following features from the requirements
engineering viewpoint:
• a dynamic, rich editing environment for team members to capture and manage
requirements
• to create a centralised repository
• to create task-driven workflow to do change management, and defect tracking.
But, what is a good process of Requirements Engineering for the CASE?

36
A simple four-step process for requirements engineering is given in Figure 3.3. Case Tools

Requirement
Elicitation

Requirements
Requirement Specification
Management
Engineering

Validation

Figure 3.3: The four-step requirement engineering process

Requirement Elicitation
A simple technique for requirements elicitation is to ask “WHY”.
CASE tools support a dynamic, yet intuitive, requirements capture and management
environment that supports content and its editing. Some of the features available for
requirement elicitation are:
• Reusable requirements and design templates for various types of system
• Keeping track of important system attributes like performance and security
• It may also support a common vocabulary of user-defined terms that can be
automatically highlighted to be part of glossary.
• Provide feature for the assessment of the quality of requirements
• Separate glossary for ambiguous terms that can be flagged for additional
clarification.
What do we expect from the tool?
• It should have rich support for documentation that is easily understandable to
stakeholders and development teams.
• It should have the capability of tracking of requirements during various SDLC
systems.
• It should help in the development of standard technical and business
terminology for end clients.
Software Analysis and Specification

One of the major reasons of documenting requirements is to remove the ambiguity of

information. A good requirement specification is testable for each requirement.

One of the major features supported by CASE tools for specification is that the design
and implementation should be traceable to requirements. A good way to do so is to
support a label or a tag to the requirements. In addition it should have the following
features:

• Must have features for storing and documenting of requirements.

• Enable creation of models that are critical to the development of functional
requirements.
• Allow development of test cases that enable the verification of requirements and
their associated dependencies.
• Test cases help in troubleshooting the correlation between business
requirements and existing system constraints.

37
Advanced Software What do we expect from the tool?
Engineering
• It should allow development of a labeled requirements document that helps in
traceability of requirements.
• It should allow both functional and non-functional requirements with related
quality attributes to be made.
• We should be able to develop the associated models.

Figure 3.4: A sample DFD using CASE Tools

“The automated approach of

software development needs
to have a spirit of
collaboration, bringing
together world-renowned
principal investigators,
business analysts, and
software development
teams.”

Figure 3.5: A Sample ER Diagram using CASE Tools

Figures 3.4 and 3.5 show some of the models developed with the help of a sample
CASE Tool.

38
Validation of Requirements Case Tools

A very important feature in this regard is to allow collaboration yet customizable

workflows for the software development team members. Also facilitating approvals
and electronic signatures to facilitate audit trails. Assigning owner of requirement may
be helpful if any quality attributes may need changes. Thus, a prioritised validated
documented and approved requirements can be obtained.
Managing Requirements
The requirements document should have visibility and help in controlling the software What are the features of high
delivery process. Some such features available in CASE tools are: quality requirements?

• estimation of efforts and cost • Correctness

• specification of project schedule such as deadline, staff requirements and other • Unambiguous
constraints • Must
• specification of quality parameters. • Consistency
• Known constraints
Software Change Management • Modifiable
An incomplete or ambiguous requirement if detected early in the analysis phase can • Priority Assigned
be changed easily with minimum cost. However, once they are converted to baselines • Traceable
after requirements validations the change should be controlled. • Verifiable
One of the major requirements of change management is:
Any change to these requirements should follow a process which is defined as the
ability to track software requirements and their associated models/documents, etc.
(e.g., designs, DFDs and ERDs, etc.). This helps in determining the components that
will be impacted due to change. This also helps tracking and managing change. The
whole process starts with labeling the requirements properly.

Most CASE Tools store requirement baselines, including type, status, priority and
change history of a software item. Such traceability may be bi-directional in nature.

Static word processing documents or spreadsheet recedes communication issues

because those tools do not allow sharing and collaboration on up-to-date
requirements. To overcome this a CASE enabled requirements management
infrastructure offers the familiarity of environments such as Microsoft Word, with
added communication methods, such as email. Thus, CASE is a very useful tool for
requirement engineering.

3.5 CASE TOOLS AND DESIGN AND

IMPLEMENTATION
In general, some CASE tools support the analysis and design phases of software
development. Some of the tools supported by the design tools are:

• Structured Chart.
• Pogram Document Language (PDL).
• Optimisation of ER and other models.
• Flow charts.
• Database design tools.
• File design tools.
Some of functions that these diagrams tool support are simple but are very
communicative as far as representations of the information of the analysis and design
phases are concerned. CASE Tools also support standard representation of program
architecture; they also contain testing items related to the design and debugging.
Automatic support for maintenance is provided in case any of the requirements or
design items is modified using these diagrams. These CASE tools also support
39
Advanced Software error-checking stages. They allow checks for completeness and consistency of the
Engineering
required functional design types and consistency at various levels of cross referencing
among the documents consistency checking for these documents during the
requirements analysis and design phases.
Proper modeling helps in proper design architecture. All the CASE tools have strong
support for models. They also help in resolving conflicts and ambiguity among the
models and help in optimising them to create excellent design architecture and process
implementation.
But why do we need to model?
Can you understand code? If you understand it, then why would you call it code?

The major advantages for modeling are:

A model enhances communication, as it is more pictorial and less code.
Even early humans have used pictures to express ideas in a better way.

Figure 3.6: Model versus code

A model
• helps the users
• may reduce the cost of project
• can convey a broad spectrum of information.
Some standard models may need to represent:
• Overall system architecture of the software
• Software dependencies
• Flow of information through a software system
• Database organisation and structure.
• Deployment configuration, etc.

Models also help in better planning and reduction of risk as one can make top down
models, thus controlling complexity.

So what is a good modeling tool?

The following are some of the characteristics of a good modeling tool:

CASE tools provide continuously synchronized models and code, thus also help in
consistent understanding of information and documentation. It also helps other
software developers to understand the portions and relationships to portions other
team members are working on.
Help in management of source code through a more visual model.

40
Refactoring of the code allows a re-look and improvement of code, as modeling tools Case Tools
contains, thus are most continuously sychronised code and models suitable for
refactoring.

Modeling can help in creating good patterns including modeling patterns, language
specific patterns and basic patterns for common operations such as implementing
interfaces, etc.
Models also facilitate reverse engineering.
Given the task of maintaining software that was built by a team that has moved on to a
new project, there may be very little documentation available for the project.

The value of a modeling tool can be tremendous in such cases. The developer can take
the existing code, create models for it to understand the software. This can save a lot
of time for the developer.
A modeling tool should have been integrated with requirements tools, so that
architects see consistently unambiguous information.

Figure 3.7: A State Model

CASE Repository
CASE Repository stores software system information. It includes analysis and design
specifications and helps in analysing these requirements and converting them into
program code and documentation. The following is the content of CASE repository:
• Data
• Process
• Models
• Rules/ Constraints.
Data: Information and entities/object relationship attributes, etc.

Process: Support structured methodology, link to external entities, document

structured software development process standards.

Models: Flow models, state models, data models, UML document etc.

Rules/Constraints: Business rules, consistency constraints, legal constraints.

41
Advanced Software The CASE repository has two primary segments.
Engineering
1. Information repository
2. Data dictionary.
Information Repository includes information about an organisation’s business
information and its applications.
The CASE tools manage and control access to repository. Such information data can
also be stored in corporate database.
Data dictionary contains all the data definitions for all organisational applications,
along with cross-referencing if any.
Its entries have a standard definition, viz., element name and alias; textual description
of the element; related elements; element type and format; range of acceptable values
and other information unique to the proper processing of the element.

CASE Repository has additional advantages such that it assists the project
management tasks; aids in software reusability by enabling software modules in a
manner so that they can be used again.
Implementation tools and CASE
CASE tools provide the following features for implementation:
• Diagramming tools enable visual representation of a system and its components
• Allow representing process flows.
• Help in implementing the data structures and program structures
• Support automatic creation of system forms and reports.
• Ready prototype generation.
• Create of both technical and user documentation.
• Create master templates used to verify documentation and its conformance to all
stages of the Software Development Life Cycle (SDLC).
• Enable the automatic generation of program and database from the design
documents, diagrams, forms and reports stored in the repository.

3.6 SOFTWARE TESTING

CASE tools may also support software testing. One of the basic issues of testing is
management, execution and reporting. Testing tools can help in automated unit
testing, functional regression testing, and performance testing. A testing tool ensures
the high visibility of test information, types of common defects, and application
readiness.
Features Needed for Testing
The tool must support all testing phases, viz., plan, manage and execute all types of
tests viz., functional, performance, integration, regression, testing from the same
interface.
It should integrate with other third party testing tools.
It should support local and remote test execution.
It should help and establish and manage traceability by linking requirements to test
cases. This also helps when requirements change; in such as case the test cases traced
to the requirement are automatically flagged as possible candidates for change.
42
It should create a log of test run. Case Tools

It should output meaningful reports on test completeness, test analysis.

It may provide automated testing.
) Check Your Progress 2
1) List any four tools that are used in web software engineering but are not used in
general software projects.
……………………………………………………………………………………
……………………………………………………………………………………
2) Which of the requirements engineering processes is not supported by CASE
tools?
……………………………………………………………………………………
……………………………………………………………………………………

3) List any four major requirements of a design tool.

……………………………………………………………………………………
……………………………………………………………………………………

4) List four important features of a testing tool.

……………………………………………………………………………………
.…………………………………………………………………………………...

3.7 SOFTWARE QUALITY AND CASE TOOLS

Software quality is sacrificed by many developers for more functionality, faster
development and lower cost. However, one must realise that a good quality product
actually enhances the speed of software development. It reduces the cost and allows
enhancement and functionality with ease as it is a better structured product. You need
to pay for a poor quality in terms of more maintenance time and cost. Can the good
quality be attributed to a software by enhancing the testing? The answer is NO. The
high quality software development process is most important for the development of
quality software product. Software quality involves functionality for software
usability, reliability, performance, scalability, support and security.
Integrated CASE tools:
• help the development of quality product as they support standard methodology
and process of software development
• supports an exhaustive change management process
• contains easy to use visual modeling tools incorporating continuous quality
assurance.
Quality in such tools is represented in all life cycle phases viz., Analysis/ Design
development, test and deployment. Quality is essential in all the life cycle phases.
Analysis: A poor understanding of analysis requirements may lead to a poor product.
CASE tools help in reflecting the system requirements clearly, accurately and in a
simple way. CASE tools support the requirements analysis and coverage also as we
have modeling. CASE also helps in ambiguity resolution of the requirements, thus
making high quality requirements.

Design: In design the prime focus of the quality starts with the testing of the
architecture of the software. CASE tools help in detecting, isolating and resolving
structure deficiency during the design process. On an average, a developer makes 100
to 150 errors for every thousand lines of code. Assuming only 5% of these errors are

43
Advanced Software serious, if software has ten thousand lines of code you may still have around 50
Engineering
serious coding errors in your system. One of the newer software development
processes called the Agile process helps in reducing such problems by asking the
developer to design their test items first before the coding.
A very good approach that is supported by CASE tools specially running time
development of C, C++, JAVA or .NET code is to provide a set of automatic run time
Language tools for development of reliable and high performance applications.
Testing: Functionality and performance testing is an integrated part of ensuring high
quality product. CASE support automated testing tools that help in testing the
software, thus, helping in improving the quality of testing. CASE tools enhance the
speed breadth and reliability of these design procedures. The design tools are very
important specifically in case of a web based system where scalability and reliability
are two major issues of design.
Deployment: After proper testing a software goes through the phase of deployment
where a system is made operational. A system failure should not result in a complete
failure of the software on restart. CASE tools also help in this particular place. In
addition, they support configuration management to help any kind of change thus to
be made in the software.
Quality is teamwork: It involves integration of workflow of various individuals. It
establishes a traceability and communication of information, all that can be achieved
by sharing workload documents keeping their configuration items.

3.8 SOFTWARE CONFIGURATION

MANAGEMENT
Software Configuration Management (SCM) is extremely important from the view of
deployment of software applications. SCM controls deployment of new software
versions. Software configuration management can be integrated with an automated
solution that manages distributed deployment. This helps companies to bring out new
releases much more efficiently and effectively. It also reduces cost, risk and
accelerates time.
A current IT department of an organisation has complex applications to manage.
These applications may be deployed on many locations and are critical systems.
Thus, these systems must be maintained with very high efficiency and low cost and
time. The problem for IT organisations has increased tremendously as some of the
organisations may need to rebuild and redeploy new software versions a week over
multi-platform global networks.

In such a situation, if rebuilding of application versions is built or deployed manually

using a spreadsheet, then it requires copying of rebuilt software to many software
locations, which will be very time consuming and error prone. What about an
approach where newer software versions are automatically built and deployed into
several distributed locations through a centralised control. For example, assume that
IGNOU has a data entry software version 1.0 for entering assignment marks which is
deployed all the RCs. In case its version 1.1 is to be deployed, if the re-built software
need to be sent and deployed manually, it would be quite troublesome. Thus, an
automatic deployment tool will be of great use under the control of SCM.
What do we need?
We need an effective SCM with facilities of automatic version control, access control,
automatic re-building of software, build audit, maintenance and deployment. Thus,
SCM should have the following facilities:
• Creation of configuration

44
• This documents a software build and enables versions to be reproduced on Case Tools
demand
• Configuration lookup scheme that enables only the changed files to be rebuilt.
Thus, entire application need not be rebuilt.
• Dependency detection features even hidden dependencies, thus ensuring correct
behaviour of the software in partial rebuilding.
• Ability for team members to share existing objects, thus saving time of the team
members.
Figure 3.8 shows a simple Configuration Management based rebuilding and
deployment process.

Approval Configuration
An SCM Completion status Test management
Environment Environment support for
automatic
deployment

Version Package
controlled ready for
software deployment
build

Figure 3.8: Simple configuration management environment

3.9 SOFTWARE PROJECT MANAGEMENT AND

CASE TOOLS
Developing commercial software is not a single-player activity. It is invariably a
collaborative team activity. The development of business-critical systems are also too
risky, or are too large for a single developer to deliver the product in a stipulated time
and quality frame.

A software team involves designers, developers, and testers who work together for
delivering the best solution in the shortest time. Sometimes, these teams can be
geographically dispersed. Managing such a team may be a major change requests, and
task management.

The CASE tools help in effective management of teams and projects. Let us look into
some of the features of CASE in this respect:

• Sharing and securing the project using the user name and passwords.
• Allowing reading of project related documents
• Allowing exclusive editing of documents
• Linking the documents for sharing
• Automatically communicative change requests to approver and all the persons
who are sharing the document.
• You can read change requests for yourself and act on them accordingly.
• Setting of revision labels so that versioning can be done.
• Any addition or deletion of files from the repository is indicated.
• Any updating of files in repository is automatically made available to users.
• Conflicts among versions are reported and avoided
• Differences among versions can be visualized.

45
Advanced Software • The linked folder, topics, and change requests to an item can be created and
Engineering
these items if needed can be accessed.
• It should have reporting capabilities of information
The project management tools provide the following benefits:
• They allow control of projects through tasks so control complexity.
• They allow tracking of project events and milestones.
• The progress can be monitored using Gantt chart.
• Web based project related information can be provided.
• Automatic notifications and mails can be generated.

Some of the features that you should look into project management software are:
• It should support drawing of schedules using PERT and Gantt chart.
• It should be easy to use such that tasks can be entered easily, the links among
the tasks should be easily desirable.
• Milestones and critical path should be highlighted.
• It should support editing capabilities for adding/deleting/moving tasks.
• Should map timeline information against a calendar.
• Should allow marking of durations for each task graphically.
• It should provide views tasks, resources, or resource usage by task.
• Should be useable on network and should be able to share information through
network.
) Check Your Progress 3
1) How do CASE tools support quality?
……………………………………………………………………………………
……………………………………………………………………………………

2) What is the role of CASE in software configuration management?

………………………………………………………………………………
………………………………………………………………………………….

3) Can CASE tools result in perfect project management?

……………………………………………………………………………………
……………………………………………………………………………………

3.10 SUMMARY
This unit provides an introduction to CASE tools in action. The CASE tools are
primarily used to automate the stages of the Software Development Life Cycle. It
automates most of the tasks of software engineering such as requirements analysis,
modeling, designing, support for testing, and implementation, project management,
software configuration management, software quality management, etc. CASE tools
also help in traceability of requirements. They are useful tools for reverse engineering.
Presently, many CASE tools which integrate the complete Software Development Life
Cycle are available and can be deployed successfully in an organisation. These CASE
tools support standard methodology, provide flexibility of environment, strong
integration of various software development stages, reverse engineering, project
management, and configuration management under one single environment.
However, it is to be noted that all deployments of CASE have not succeeded.
46
Successful CASE tools are those which are simple to use support standard Case Tools
methodology, and reverse engineering and have a strong vendor support including
training.

3.11 SOLUTIONS/ANSWERS
Check Your Progress 1
1) CASE tools are needed for
• Development of cost effective software
• Minimisation of development time
• Standardising the software development process
• Avoiding repetition and maximising reuse
• Development of better quality product
• Collaborative developments etc.

2) CASE tools
• Follow standard methodology
• Allow integration of information
• Allow traceability
• Help improving of quality
• Reduce cost
• Support reverse engineering
• Provide on-line help
• Check for inconsistency of information
• Provide tools for configuration management and project management.

Check Your Progress 2

1) Web security test tools, link checkers, site optimization tools, server
management tools
2) Although requirements engineering phases viz., requirement elicitation,
specification, validation, requirements management, have some part being
played by CASE tools, yet it is the stage of requirement elicitation where
CASE tools are least helpful as this stage requires interaction with the users.
3) The design tools support the following:
a. A strong consistent data dictionary
b. Support for presenting design architecture and data design.
c. Support for traceability and integration with test scenarios
d. Optimisation of models and process flow charts.

4) Test planning, Integration with automatic testing tool, Traceability,

Flagging the possible candidates for change.
Check Your Progress 3
1) The quality of the software is supported at all the Life Cycle stages of
software development with the help of CASE tools. For example, in the
analysis phase CASE tools may automatically flag requirement ambiguity in

47
Advanced Software the design phase they may point out any inconsistency, in the test phase they
Engineering
may point out the reliability of software, etc.
2) CASE tools control the baseline configuration items thus support a strict
change control such that any changes made during any life cycle phase results
in automatic flagging of the various documents of various stages of SDLC
affected by that change. They also help in version control.
3) No. They are only predictors of various failures to meet the schedule of the
project.

3.12 FURTHER READINGS

1) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson

Education.
2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman;
McGraw-Hill International Edition.
Reference Websites
• http://www.rspa.com
• http://www.ieee.org

48
 Advanced Topics in
UNIT 4 ADVANCED TOPICS IN SOFTWARE Software Engineering

ENGINEERING
Structure Page Nos.
4.0 Introduction 49
4.1 Objectives 50
4.2 Evolution of Formal Methods 50
4.3 Use of Mathematics in Software Development 51
4.4 Formal Methods 51
4.4.1 What Can Be Formally Specified?
4.4.2 Goals of Formal Specification
4.5 Application Areas 53
4.6 Limitations of Formal Specification Using Formal Methods 54
4.7 Cleanroom Software Engineering 55
4.8 Conventional Software Engineering Models Vs. Cleanroom Software
Engineering Model 56
4.9 Cleanroom Software Engineering Principles, Strategy and
Process Overview 56
410 Limitations of Cleanroom Engineering 57
4.11 Similarities and Differences between Cleanroom and OO Paradigm 58
4.12 Software Reuse and its Types 58
4.13 Why Component based Software Engineering? 59
4.14 Component based Software Engineering (CBSE) Process 60
4.14.1 Domain Engineering
4.14.2 Component based Development
4.15 Component Technologies Available 62
4.16 Challenges for CBSE 62
4.17 Reengineering: An Introduction 64
4.18 Objectives of Reengineering 64
4.19 Software Reengineering Life Cycle 65
4.20 Summary 66
4.21 Solutions / Answers 67
4.22 Further Readings 68
4.23 Glossary 68

4.0 INTRODUCTION
In the first few units we have studied the various methods for conventional software
engineering. Software engineering methods can be categorised on a “formality
spectrum.” The analysis and design methods discussed previously would be placed at
the informal to moderately rigorous end of the spectrum. In these methods, a
combination of diagrams, text, tables, and simple notation is used to create analysis
and design models.
At the other end of the formality spectrum are formal methods, which are completely
mathematical in form. A specification and design are described using a formal syntax
and semantics that specify system function and behaviour. Other specialised models
being the Cleanroom software engineering, component-based software engineering,
re-engineering and reverse engineering.
Harlan Mills has developed the Cleanroom software engineering methodology, which
is an approach for integrating formal methods into the lifecycle. The Cleanroom
approach combines formal methods and structured programming with Statistical
Process Control (SPC), the spiral lifecycle and incremental releases, inspections, and
software reliability modeling. It fosters attitudes, such as emphasising defect
prevention over defect removal, that are associated with high quality products in non-
software fields.
49
 Advanced Software In most engineering disciplines, systems are designed by composition (building
Engineering
system out of components that have been used in other systems). Software
engineering has focused on custom development of components. To achieve better
software quality, more quickly, at lower costs, software engineers are beginning to
adopt systematic reuse as a design process. There are various ways to achieve this and
one of the models is the Component-based software engineering.
Let us study the various specialised software engineering models like the formal
method, Cleanroom engineering, component-based engineering, re-engineering and
reverse engineering in this unit.

4.1 OBJECTIVES
After going through this unit, you should be able to:
• understand the pitfalls of the conventional software engineering;
• know various advanced methods of software engineering – their advantages and
drawbacks;
• describe the methodology of formal methods and Cleanroom software
engineering, and
• discuss the Re-engineering and Reverse engineering process.

4.2 EVOLUTION OF FORMAL METHODS

The seventies witnessed the structured programming revolution. After much debate,
software engineers became convinced that better programs result from following
certain precepts in program design. Recent imperative programming languages
provide constructs supporting structured programming. Achieving this consensus did
not end debate over programming methodology. On the contrary, a period of
continuous change began, with views on the best methods of software development
mutating frequently. Top-down development, modular decomposition, data
abstraction, and, most recently, object oriented design are some of the jargon terms
that have arisen to describe new concepts for developing large software systems. Both
researchers and practitioners have found it difficult to keep up with this onslaught of
new methodologies.
There is a set of core ideas that lies at the base of these changes. Formal methods have
provided a unifying philosophy and central foundation upon which these
methodologies have been built. Those who understand this underlying philosophy can
more easily adopt these and other programming techniques.
One way to improve the quality of software is to change the way in which software is
documented: at the design stage, during development, and after release. Existing
methods of documentation offer large amounts of text, pictures, and diagrams, but
these are often imprecise and ambiguous. Important information is hidden amongst
irrelevant details, and design flaws are discovered too late, making them expensive or
impossible to correct.
There is an alternative. Formal methods, based upon elementary mathematics, can be
used to produce precise, unambiguous documentation, in which information is
structured and presented at an appropriate level of abstraction. This documentation
can be used to support the design process, and as a guide to subsequent development,
testing, and maintenance.
It seems likely that the use of formal methods will become standard practice in
software engineering. The mathematical basis is different from that of civil or
mechanical engineering, but it has the same purpose: to add precision, to aid
understanding, and to reason about the properties of a design. Whatever the discipline,
the use of mathematics can be expensive, but it is our experience that it can actually
reduce costs.
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Existing applications of formal methods include: the use of the probability theory in Advanced Topics in
Software Engineering
performance modeling; the use of context-free grammars in compiler design; the use
of the relational calculus in database theory. The formal method described in this book
has been used in the specification and design of large software systems. It is intended
for the description of state and state-based properties, and includes a theory of
refinement that allows mathematics to be used at every stage of program development.
Let us see the details of the Formal methods in the next section.

4.3 USE OF MATHEMATICS IN SOFTWARE

DEVELOPMENT
Mathematics supports abstraction and therefore is a powerful medium for modeling.
Because they are exact, mathematical specifications are unambiguous and can be
validated to uncover contradictions and incompleteness. It allows a developer to
validate a specification for functionality. It is possible to demonstrate that a design
matches a specification, and that some program code is a correct reflection of a
design.
How is the mathematics of formal languages applied in software development? What
engineering issues have been addressed by their application? Formal methods are of
global concern in software engineering. They are directly applicable during the
requirements, design, and coding phases and have important consequences for testing
and maintenance. They have influenced the development and standardisation of many
programming languages, the programmer’s most basic tool. They are important in
ongoing research that may change standard practice, particularly in the areas of
specifications and design methodology. They are entwined with lifecycle models that
may provide an alternative to the waterfall model, namely rapid prototyping, the
Cleanroom variant on the spiral model, and “transformational” paradigms. The
concept of formalism in formal methods is borrowed from certain trends in 19th and
20th century mathematics. Formal methods are merely an adoption of the axiomatic
method, as developed by these trends in mathematics, for software engineering.
Mastery of formal methods in software requires an understanding of this mathematics
background. Mathematical topics of interest include formal logic, both the
propositional calculus and predicate logic, set theory, formal languages, and automata
such as finite state machines.

4.4 FORMAL METHODS

A formal method in software development is a method that provides a formal
language for describing a software artifact (e.g., specifications, designs, source code)
such that formal proofs are possible, in principle, about properties of the artifact so
expressed.
The definition is based on two essential components. First, formal methods involve
the essential use of a formal language. A formal language is a set of strings over some
well-defined alphabet. Rules are given for distinguishing those strings, defined over
the alphabet, that belong to the language from strings that do not. Secondly, formal
methods in software support formal reasoning about formulae in the language. These
methods of reasoning are exemplified by formal proofs. A proof begins with a set of
axioms, which are to be taken as statements postulated to be true. Inference rules state
that if certain formula, known as premises, are derivable from the axioms, then
another formula, known as the consequent, is also derivable. A set of inference rules
must be given in each formal method. A proof consists of a sequence of well-defined
formulae in the language in which each formula is either an axiom or derivable by an
inference rule from previous formulae in the sequence. The last formula in the
sequence is said to be proven.

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 Advanced Software The major concerns of the formal methods are as follows:
Engineering
i) The correctness of the problem
o producing software that is “correct” is famously difficult;
o by using rigorous mathematical techniques, it may be possible to make
probably correct software.
ii) Programs are mathematical objects
o they are expressed in a formal language;
o they have a formal semantics;
o programs can be treated as mathematical theories.
Formal methods support precise and rigorous specifications of those aspects of a
computer system capable of being expressed in the language. Since defining what a
system should do, and understanding the implications of these decisions, are the most
troublesome problems in software engineering, this use of formal methods has major
benefits. In fact, practitioners of formal methods frequently use formal methods solely
for recording precise specifications, not for formal verifications.
Formal methods were originally developed to support verifications, but higher interest
currently exists in specification methods. Several methods and languages can be used
for specifying the functionality of computer systems. No single language, of those
now available, is equally appropriate for all methods, application domains, and
aspects of a system. Thus, users of formal specification techniques need to understand
the strength and weaknesses of different methods and languages before deciding on
which to adopt. The distinction between a specification method and a language is
fundamental. A method states what a specification must say. A language determines
in detail how the concepts in a specification can be expressed. Some languages
support more than one method, while most methods can be used in several
specification languages.
Some of the most well-known formal methods consist of or include specification
languages for recording a system’s functionality. These methods include:
• Z (pronounced “Zed”)
• Communicating Sequential Processes (CSP)
• Vienna Development Method (VDM)
• Larch
• Formal Development Methodology (FDM)
4.4.1 What can be Formally Specified?
Formal methods can include graphical languages. Data Flow Diagrams (DFDs) are the
most well-known graphical technique for specifying the function of a system. DFDs
can be considered a semi-formal method, and researchers have explored techniques
for treating DFDs in a completely formal manner. Petri nets provide another well-
known graphical technique, often used in distributed systems. Petri nets are a fully
formal technique.
Finally, finite state machines are often presented in tabular form. This does not
decrease the formalism in the use of finite state machines. So the definition of formal
methods provided earlier is quite encompassing.
Software engineers produce models and define the properties of systems at several
levels of abstraction. Formal methods can be employed at each level. A specification
should describe what a system should do, but not how it is done. More details are
provided in designs, with the source code providing the most detailed model.
For example, Abstract Data Types (ADTs) frequently are employed at intermediate
levels of abstraction. ADTs, being mathematical entities, are perfect candidates for
formal treatment and are often so treated in the literature.
Formal methods are not confined to the software components of large systems.
System engineers frequently use formal methods. Hardware engineers also use formal
methods, such as VHSIC Hardware Description Language (VHDL) descriptions, to
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model integrated circuits before fabricating them. The following section lists the goals Advanced Topics in
Software Engineering
of the formal specification.
4.4.2 Goals of Formal Specification
Once a formal description of a system has been produced, what can be done with it?
Usable formal methods provide a variety of techniques for reasoning about
specifications and drawing implications. The completeness and consistency of a
specification can be explored. Does a description imply a system should be in several
states simultaneously? Do all legal inputs yield one and only one output? What
surprising results, perhaps unintended, can be produced by a system? Formal methods
provide reasoning techniques to explore these questions. Do lower level descriptions
of a system properly implement higher level descriptions? Formal methods support
formal verification, the construction of formal proofs that an implementation satisfies
a specification. The possibility of constructing such formal proofs was historically the
principal driver in the development of formal methods. Prominent technology for
formal verification includes E Dijkstra's “weakest precondition” calculus and Harlan
Mills’ “functional correctness” approach which we are not going to discuss here. The
following are the goals of the formal specification:
• Removal of ambiguity: The formal syntax of a specification language enables
requirements or design to be interpreted in only one way, eliminating the
ambiguity that often occurs when using natural language. Removes ambiguity
and encourages greater rigour in the early stages of the software engineering
process.
• Consistency: Facts stated in one place should not be contradicted in
another. This is ensured by mathematically proving that initial facts can be
formally mapped (by inference) into later statements later in the specification.
• Completeness: This is difficult, even when using formal methods. Some
aspects of a system may be left undefined by mistake or by intention. It is
impossible to consider every operational scenario in a large, complex system.

4.5 APPLICATION AREAS

Formal methods can be used to specify aspects of a system other than functionality.
Software safety and security are other areas where formal methods are sometimes
applied in practice. The benefits of proving that unsafe states will not arise, or security
will not be violated, can justify the cost of complete formal verifications of the
relevant portions of a software system. Formal methods can deal with many other
areas of concern to software engineers, but have not been much used, other than in
research organisations, for dealing with issues unrelated to functionality, safety, and
security. Areas in which researchers are exploring formal methods include fault
tolerance, response time, space efficiency, reliability, human factors, and software
structure dependencies. The following are the Formal specifications application areas:
• safety critical systems
• security systems
• The definition of standards
• Hardware development
• Operating systems
• Transaction processing systems
• Anything that is hard, complex, or critical.

Let us see the drawbacks of the formal specifications in the next section.

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 Advanced Software
Engineering 4.6 LIMITATIONS OF FORMAL SPECIFICATION
USING FORMAL METHODS
Some problems exist, however formal specification focuses primarily on function and
data. Timing, control, and behavioural aspects of a problem are more difficult to
represent. In addition, there are elements of a problem (e.g., HCI, the human-machine
interface) that are better specified using graphical techniques. Finally, a specification
using formal methods is more difficult to learn than other analysis methods. For this
reason, it is likely that formal mathematical specification techniques will be
incorporated into a future generation of CASE tools. When this occurs,
mathematically-based specification may be adopted by a wider segment of the
software engineering community. The following are the major drawbacks:
Cost: It can be almost as costly to do a full formal specification as to do all the coding.
The solution for this is, don’t formally specify everything, just the subsystems you
need to (hard, complex, or critical).
Complexity: Not everybody can read formal specifications (especially customers and
users). The solution is to provide a very good and detailed documentation. No one
wants to read pure formal specifications–formal specifications should always be
interspersed with natural language (e.g. English) explanation.
Deficiencies of Less Formal Approaches: The methods of structured and object-
oriented design discussed previously make heavy use of natural language and a
variety of graphical notations. Although careful application of these analysis and
design methods can and does lead to high–quality software, sloppiness in the
application of these methods can create a variety of problems which are:
• Contradictions: statements that are at variance with one another.
• Ambiguities : statements that can be interpreted in a number of ways
• Vagueness : statements that lack precision, and contribute little information.
• Incomplete statements : a description is not functionally complete.
• Mixed levels of abstraction : statements with high and low levels of detail are
interspersed, which can make it difficult to comprehend the functional
architecture.
This method gained popularity among the software developers who must build safety-
critical software like aircraft avionics and medical devices. But the applicability in the
business environment has not clicked.
Let us study the Cleanroom Software Engineering in the next section.

) Check Your Progress 1

1) What are Formal methods?
……………………………………………………………………………………
……………………………………………………………………………………

2) What are the main parts of the Formal methods?

……………………………………………………………………………………
……………………………………………………………………………………

4.7 CLEANROOM SOFTWARE ENGINEERING

Cleanroom software engineering is an engineering and managerial process for the
development of high-quality software with certified reliability. Cleanroom was
originally developed by Dr. Harlan Mills. The name “Cleanroom” was taken from the
electronics industry, where a physical clean room exists to prevent introduction of
defects during hardware fabrication. It reflects the same emphasis on defect
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prevention rather than defect removal, as well as Certification of reliability for the Advanced Topics in
Software Engineering
intended environment of use. It combines many of the formal methods and software
quality methods we have studied so far. The focus of Cleanroom involves moving
from traditional software development practices to rigorous, engineering-based
practices.
Cleanroom software engineering yields software that:
• Is correct by mathematically sound design
• Is certified by statistically-valid testing
• Reduces the cycle time results from an incremental development strategy and
the avoidance of rework
• Is well-documented
• Detects errors as early as possible and reduces the cost of errors during
development and the incidence of failures during operation; thus the overall life
cycle cost of software developed under Cleanroom can be expected to be far
lower than the industry average.
The following principles are the foundation for the Cleanroom-based software
development:
Incremental development under statistical quality control (SQC): Incremental
development as practiced in Cleanroom provides a basis for statistical quality control
of the development process. Each increment is a complete iteration of the process, and
measures of performance in each increment (feedback) are compared with
pre-established standards to determine whether or not the process is “in control.” If
quality standards are not met, testing of the increment ceases and developers return to
the design stage.
Software development based on mathematical principles: In Cleanroom software
engineering development, the key principle is that, a computer program is an
expression of a mathematical function. The Box Structure Method is used for
specification and design, and functional verification is used to confirm that the design
is a correct implementation of the specification. Therefore, the specification must
define that function before design and functional verification can begin. Verification
of program correctness is performed through team review based on correctness
questions. There is no execution of code prior to its submission for independent
testing.
Software testing based on statistical principles: In Cleanroom, software testing is
viewed as a statistical experiment. A representative subset of all possible uses of the
software is generated, and performance of the subset is used as a basis for conclusions
about general operational performance. In other words, a “sample” is used to draw
conclusions about a “population.” Under a testing protocol that is faithful to the
principles of applied statistics, a scientifically valid statement can be made about the
expected operational performance of the software in terms of reliability and
confidence.

4.8 CONVENTIONAL SOFTWARE

ENGINEERING MODELS Vs. CLEANROOM
SOFTWARE ENGINEERING MODEL
Cleanroom has been documented to be very effective in new development and
reengineering like whole systems or major subunits. The following points highlight
the areas where Cleanroom affects or differs from more conventional software
development engineering practice:
Small team of software engineers: A Cleanroom project team is small, typically six
to eight qualified professionals, and works in an organised way to ensure the
intellectual control of work in progress. The composition of the Cleanroom Process
Teams are as follows:
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 Advanced Software • Specification team develops and maintains the system specification
Engineering
• Development team develops and verifies software
• Certification team develops set of statistical tests to exercise software after
development and reliability growth models used to assess reliability.
Time allocation across the life cycle phases: Because one of the major objectives of
Cleanroom is to prevent errors from occurring, the amount of time spent in the design
phase of a Cleanroom development is likely to be greater than the amount of time
traditionally devoted to design.
Existing organisational practices: Cleanroom does not preclude using other software
engineering techniques as long as they are not incompatible with Cleanroom
principles. Implementation of the Cleanroom method can take place in a gradual
manner. A pilot project can provide an opportunity to “tune” Cleanroom practices to
the local culture, and the new practices can be introduced as pilot results to build
confidence among software staff.
The following are some of the examples of the projects implemented using the
Cleanroom engineering method:
• IBM COBOL/SF product
• Ericsson OS-32 operating system project
• USAF Space Command and Control Architectural Infrastructure (SCAI)
STARS Demonstration Project at Peterson Air Force Base in Colorado Springs,
Colorado.
• US Army Cleanroom project in the Tank-automotive and Armaments
Command at the U.S. Army Picatinny Arsenal.

4.9 CLEANROOM SOFTWARE ENGINEERING

PRINCIPLES, STRATEGY AND PROCESS
OVERVIEW
This software development is based on mathematical principles. It follows the box
principle for specification and design. Formal verification is used to confirm
correctness of implementation of specification. Program correctness is verified by
team reviews using questionnaires. Testing is based on statistical principles. The test
cases are randomly generated from the usage model –failure data is interpreted using
statistical models. The following is the phase-wise strategy followed for Cleanroom
software development.
Increment planning: The project plan is built around the incremental strategy.
Requirements gathering: Customer requirements are elicited and refined for each
increment using traditional methods.
Box structure specification: Box structures isolate and separate the definition of
behaviour, data, and procedures at each level of refinement.
Formal design: Specifications (black-boxes) are iteratively refined to become
architectural designs (state-boxes) and component-level designs (clear boxes).
Correctness verification: Correctness questions are asked and answered, formal
mathematical verification is used as required.
Code generation, inspection, verification: Box structures are translated into program
language; inspections are used to ensure conformance of code and boxes, as well as
syntactic correctness of code; followed by correctness verification of the code.
Statistical test planning: A suite of test cases is created to match the probability
distribution of the projected product usage pattern.
Statistical use testing: A statistical sample of all possible test cases is used rather
than exhaustive testing.

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Certification: Once verification, inspection, and usage testing are complete and all Advanced Topics in
Software Engineering
defects removed, the increment is certified as ready for integration.
Figure 4.1 depicts the Cleanroom software engineering development overview:

Formally Error rework

specify
system

Define Construct Formally

Integrate
software structured verify
increment
increments program code

Develop
operational Design Test
profile statistical integrated
tests system

Figure 4.1: Overview of Cleanroom Software Engineering Development

4.10 LIMITATIONS OF CLEANROOM

ENGINEERING
The following are some of the limitations of the Cleanroom software engineering
method.
• Some people believe cleanroom techniques are too theoretical, too mathematical,
and too radical for use in real software development.
• Relies on correctness verification and statistical quality control rather than unit
testing (a major departure from traditional software development).
• Organisations operating at the ad hoc level of the Capability Maturity Model do
not make rigorous use of the defined processes needed in all phases of the
software lifecycle.

4.11 SIMILARITIES AND DIFFERENCES

BETWEEN CLEANROOM AND OO
PARADIGM
The following are the similarities and the differences between the Cleanroom software
engineering development and OO software engineering paradigm.
Similarities
• Lifecycle - both rely on incremental development
• Usage - cleanroom usage model similar to OO use case
• State Machine Use - cleanroom state box and OO transition diagram
• Reuse - explicit objective in both process models
Key Differences
• Cleanroom relies on decomposition and OO relies on composition
• Cleanroom relies on formal methods while OO allows informal use case
definition and testing
• OO inheritance hierarchy is a design resource whereas cleanroom usage
hierarchy is system itself
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 Advanced Software • OO practitioners prefer graphical representations while cleanroom practitioners
Engineering
prefer tabular representations
• Tool support is good for most OO processes, but usually tool support is only
found in cleanroom testing, not design.
Let us study the component based software engineering in the next section.

) Check Your Progress 2

1) What is Cleanroom Engineering and what are its objectives?
……………………………………………………………………………………
……………………………………………………………………………………

2) What is Statistical Process Control?

……………………………………………………………………………………
……………………………………………………………………………………
3) What are the benefits of Cleanroom software engineering?
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
4) What are the limitations of Cleanroom software engineering?
…………………………………………………………………………….
…….………………………………………………………………………

4.12 SOFTWARE REUSE AND ITS TYPES

In most engineering disciplines, systems are designed by composition (building
system out of components that have been used in other systems). Software
engineering has focused on custom development of components. To achieve better
software quality, more quickly, at lower costs, software engineers are beginning to
adopt systematic reuse as a design process. The following are the types of software
reuse:
• Application System Reuse
o reusing an entire application by incorporation of one application inside
another (COTS reuse)
o development of application families (e.g., MS Office)
• Component Reuse
o components (e.g., subsystems or single objects) of one application reused
in another application
• Function Reuse
o reusing software components that implement a single well-defined
function.
Let us take into consideration the Component Reuse type and the development
process of the components in the following sections:
“Suppose you have purchased a Television. Each component has been designed to fit
a specific architectural style – connections are standardised, a communication protocol
has been pre-established. Assembly is easy because you don’t have to build the
system from hundreds of discrete parts. Component-based software engineering
(CBSE) strives to achieve the same thing. A set of pre-built, standardised software
components are made available to fit a specific architectural style for some application
domain. The application is then assembled using these components, rather than the
“discrete parts” of a conventional programming language. Components may be
58
constructed with the explicit goal to allow them to be generalised and reused. Also, Advanced Topics in
Software Engineering
component reusability should strive to reflect stable domain abstractions, hide state
representations, be independent (low coupling) and propagate exceptions via the
component interface”.

4.13 WHY COMPONENT BASED SOFTWARE

ENGINEERING?
The goal of component-based software engineering is to increase the productivity,
quality, and decrease time-to-market in software development. One important
paradigm shift implied here is to build software systems from standard components
rather than “reinventing the wheel” each time. This requires thinking in terms of
system families rather than single systems.
CBSE uses Software Engineering principles to apply the same idea as OOP to the
whole process of designing and constructing software systems. It focuses on reusing
and adapting existing components, as opposed to just coding in a particular style.
CBSE encourages the composition of software systems, as opposed to programming
them. Two important aspects of the question are:
• Firstly, several underlying technologies have matured that permit building
components and assembling applications from sets of those components. Object
oriented and Component technology are examples – especially standards such
as CORBA.
• Secondly, the business and organisational context within which applications are
developed, deployed, and maintained has changed. There is an increasing need
to communicate with legacy systems, as well as constantly updating current
systems. This need for new functionality in current applications requires
technology that will allow easy additions.
Software Component and its types
A software component is a nontrivial, independent, and replaceable part of a system
that fulfils a clear function in the context of a well-defined architecture. In some ways,
this is similar to the description of an object in OOP. Components have an interface.
They employ inheritance rules. Components can be characterised based on their use in
the CBSE process. One category is commercial off-the-shelf (or COTS) components.
These are components that can be purchased, pre-built, with the disadvantage that
there is (usually) no source code available, and so the definition of the use of the
component given by the manufacturer, and the services which it offers, must be relied
upon or thoroughly tested, as they may or may not be accurate. The advantage, though,
is that these types of components should (in theory) be more robust and adaptable, as
they have been used and tested (and reused and retested) in many different
applications.
In addition to COTS components, the CBSE process yields:
• qualified components
• adapted components
• assembled components
• updated components.

4.14 COMPONENT BASED SOFTWARE

ENGINEERING (CBSE) PROCESS
CBSE is in many ways similar to conventional or object-oriented software
engineering. A software team establishes requirements for the system to be built using
conventional requirements elicitation techniques. An architectural design is
established. Here though, the process differs. Rather than a more detailed design task,

59
 Advanced Software the team now examines the requirements to determine what subset is directly
Engineering
amenable to composition, rather than construction.
For each requirement, we should question:
• Whether any commercial off-the-shelf (COTS) components available to
implement the requirement?
• Whether internally developed reusable components available to implement the
requirement?
• Whether interfaces for available components compatible within the architecture
of the system to be built?
The team will attempt to modify or remove those system requirements that cannot be
implemented with COTS or in-house components. This is not always possible or
practical, but reduces the overall system cost and improves the time to market of the
software system. It can often be useful to prioritise the requirements, or else
developers may find themselves coding components that are no longer necessary as
they have been eliminated from the requirements already.
The CBSE process identifies not only candidate components but also qualifies each
component’s interface, adapts components to remove architectural mismatches,
assembles components into selected architectural style, and updates components as
requirements for the system change.
Two processes occur in parallel during the CBSE process. These are:
• Domain Engineering
• Component Based Development.

4.14.1 Domain Engineering

This aims to identify, construct, catalogue, and disseminate a set of software
components that have applicability to existing and future software in a particular
application domain. An application domain is like a product family – applications
with similar functionality or intended functionality. The goal is to establish a
mechanism by which software engineers can share these components in order to reuse
them in future systems. As defined by Paul Clements, domain engineering is about
finding commonalities among systems to identify components that can be applied to
many systems and to identify program families that are positioned to take fullest
advantage of those components.
Some examples of application domains are as follows:
• Air traffic control systems
• Defence systems
• Financial market systems.
Domain engineering begins by identifying the domain to be analysed. This is achieved
by examining existing applications and by consulting experts of the type of
application you are aiming to develop. A domain model is then realised by identifying
operations and relationships that recur across the domain and therefore being
candidates for reuse. This model guides the software engineer to identify and
categorise components, which will be subsequently implemented.
One particular approach to domain engineering is Structural Modeling. This is a
pattern-based approach that works under the assumption that every application
domain has repeating patterns. These patterns may be in function, data, or behaviour
that have reuse potential. This is similar to the pattern-based approach in OOP, where
a particular style of coding is reapplied in different contexts. An example of Structural
Modeling is in Aircraft avionics: The systems differ greatly in specifics, but all
modern software in this domain has the same structural model.
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 Advanced Topics in
4.14.2 Component Based Development Software Engineering
There are three stages in this process. These are:
• Qualification,
• Adaptation (also known as wrapping),
• Composition (all in the context of components).
Component qualification: examines reusable components. These are identified by
characteristics in their interfaces, i.e., the services provided, and the means by which
consumers access these services. This does not always provide the whole picture of
whether a component will fit the requirements and the architectural style. This is a
process of discovery by the Software Engineer. This ensures a candidate component
will perform the function required, and whether it is compatible or adaptable to the
architectural style of the system. The three important characteristics looked at are
performance, reliability and usability.
Component Adaptation is required because very rarely will components integrate
immediately with the system. Depending on the component type(e.g., COTS or in-
house), different strategies are used for adaptation (also known as wrapping). The
most common approaches are:
• White box wrapping: The implementation of the component is directly
modified in order to resolve any incompatibilities. This is, obviously, only
possible if the source code is available for a component, which is extremely
unlikely in the case of COTS.
• Grey box wrapping: This relies on the component library providing a
component extension language or API that enables conflicts to be removed or
masked.
• Black box wrapping: This is the most common case, where access to source
code is not available, and the only way the component can be adapted is by pre /
post-processing at the interface level.
It is the job of the software engineer to determine whether the effort required to wrap
a component adequately is justified, or whether it would be “cheaper” (from a
software engineering perspective) to engineer a custom component which removes
these conflicts. Also, once a component has been adapted it is necessary to check for
compatibility for integration and to test for any unexpected behaviour which has
emerged due to the modifications made.
Component Composition: integrated the components (whether they are qualified,
adapted or engineered) into a working system. This is accomplished by way of an
infrastructure which is established to bind the components into an operational system.
This infrastructure is usually a library of specialised components itself. It provides a
model for the coordination of components and specific services that enable
components to coordinate with one another and perform common tasks.
There are many mechanisms for creating an effective infrastructure, in order to
achieve component composition, but in particular there is the Data Exchange Model,
which allows users and applications to interact and transfer data (an example of which
is drag-and-drop and cut-and-paste). These types of mechanisms should be defined
for all reusable components. Also important is the Underlying object model. This
allows the interoperation of components developed in different programming
languages that reside on different platforms.

4.15 COMPONENT TECHNOLOGIES AVAILABLE

Common methods of achieving this is by the use of technologies such as Corba which
allows components to communicate remotely and transparently over a network, Java
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 Advanced Software Beans and Microsoft COM which allows components from different vendors to work
Engineering
together within Windows. Sometimes it is necessary to bridge these technologies
(e.g., COM/Corba) to facilitate integration of software developed by different vendors,
or for integration with legacy systems.
It must be noted that as the requirements for a system change, components may need
to be updated. Usually, some sort of change control procedure should be in place to
facilitate configuration management, and to ensure updates to the components follow
the architectural style of the system being developed.

4.16 CHALLENGES FOR CBSE

CBSE is facing many challenges today, some of these are summarised as follows:
• Dependable systems and CBSE: The use of CBD in safety-critical domains,
real-time systems, and different process-control systems, in which the reliability
requirements are more rigorous, is particularly challenging. A major problem
with CBD is the limited possibility of ensuring the quality and other non-
functional attributes of the components and thus our inability to guarantee
specific system attributes.
• Tool support: The purpose of Software Engineering is to provide practical
solutions to practical problems, and the existence of appropriate tools is
essential for a successful CBSE performance. Development tools, such as
Visual Basic, have proved to be extremely successful, but many other tools are
yet to appear – component selection and evaluation tools, component
repositories and tools for managing the repositories, component test tools,
component-based design tools, run-time system analysis tools, component
configuration tools, etc. The objective of CBSE is to build systems from
components simply and efficiently, and this can only be achieved with extensive
tool support.
• Trusted components: Because the trend is to deliver components in binary
form and the component development process is outside the control of
component users, questions related to component trustworthiness become of
great importance.
• Component certification: One way of classifying components is to certificate
them. In spite of the common belief that certification means absolute
trustworthiness, it is in fact only gives the results of tests performed and a
description of the environment in which the tests were performed. While
certification is a standard procedure in many domains, it is not yet established in
software in general and especially not for software components.
• Composition predictability: Even if we assume that we can specify all the
relevant attributes of components, it is not known how these attributes
determine the corresponding attributes of systems of which they are composed.
The ideal approach, to derive system attributes from component attributes is still
a subject of research. A question remains - “Is such derivation at all possible?
Or should we not concentrate on the measurement of the attributes of
component composites?”
• Requirements management and component selection: Requirements
management is a complex process. A problem of requirements management is
that requirements in general are incomplete, imprecise and contradictory. In an
in-house development, the main objective is to implement a system which will
satisfy the requirements as far as possible within a specified framework of
different constraints. In component-based development, the fundamental
approach is the reuse of existing components. The process of engineering
requirements is much more complex as the possible candidate components are
usually lacking one or more features which meet the system requirements
exactly. In addition, even if some components are individually well suited to the

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Software Engineering
with others in the system- or perhaps not at all. These constraints may require
another approach in requirements engineering – an analysis of the feasibility of
requirements in relation to the components available and the consequent
modification of requirements. As there are many uncertainties in the process of
component selection there is a need for a strategy for managing risks in the
components selection and evolution process.
• Long-term management of component-based systems: As component-based
systems include sub-systems and components with independent lifecycles, the
problem of system evolution becomes significantly more complex. CBSE is a
new approach and there is little experience as yet of the maintainability of such
systems. There is a risk that many such systems will be troublesome to maintain.
• Development models: Although existing development models demonstrate
powerful technologies, they have many ambiguous characteristics, they are
incomplete, and they are difficult to use.
• Component configurations: Complex systems may include many components
which, in turn, include other components. In many cases compositions of
components will be treated as components. As soon as we begin to work with
complex structures, the problems involved with structure configuration pop up.

) Check Your Progress 3

1) What are the benefits of reuse of software?
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2) What is Commercial off the Shelf Software (COTS)?

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4.17 REENGINEERING – AN INTRODUCTION

Over the past few years, legacy system reengineering has emerged as a business
critical activity. Software technology is evolving by leaps and bounds, and in most
cases, legacy software systems need to operate on new computing platforms, be
enhanced with new functionality, or be adapted to meet new user requirements. The
following are some of the reasons to reengineer the legacy system:
• Allow legacy software to quickly adapt to changing requirements
• Comply to new organisational standards
• Upgrade to newer technologies/platforms/paradigms
• Extend the software’s life expectancy
• Identify candidates for reuse
• Improve software maintainability
• Increase productivity per maintenance programmer
• Reduce reliance on programmers who have specialised in a given software
system
• Reduce maintenance errors and costs.
Reengineering applies reverse engineering to existing system code to extract design
and requirements. Forward engineering is then used to develop the replacement
system.
Let us elaborate the definition. Reengineering is the examination, analysis, and
alteration of an existing software system to reconstitute it in a new form, and the
subsequent implementation of the new form. The process typically encompasses a
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 Advanced Software combination of reverse engineering, re-documentation, restructuring, and forward
Engineering
engineering. The goal is to understand the existing software system components
(specification, design, implementation) and then to re-do them to improve the
system’s functionality, performance, or implementation.
The reengineering process is depicted in Figure 4.2. Re-engineering starts with the
code and comprehensively reverse engineers by increasing the level of abstraction as
far as needed toward the conceptual level, rethinking and re-evaluating the
engineering and requirements of the current code, then forward engineers using a
waterfall software development life-cycle to the target system. In re-engineering,
industry reports indicate that approximately 60% of the time is spent on the reverse
engineering process, while 40% of the time is spent on forward engineering. Upon
completion of the target system, most projects must justify their effort, showing that
the necessary functionality has been maintained while quality has improved (implying
improved reliability and decreased maintenance costs).

Modification

Conceptual Re think Conceptual

Forward Engineering
System Requirements Re specify System Requirements
Reverse Engineering

Re design
System Design System Design

System Implementation Redo coding System Implementation

Existing System Compare the functionality Target System

Figure 4.2: Process of Software Reengineering

4.18 OBJECTIVES OF REENGINEERING

The objectives of a specific software reengineering activity are determined by the
goals of the clients and users of the system. However, there are two general
reengineering objectives as shown below:
• Improve quality: Typically, the existing software system is of low quality, due
to many modifications. User and system documentation is often out-of-date or
no longer in existence. Re-engineering is intended to improve software quality
and to produce current documentation. Improved quality is needed to increase
reliability, to improve maintainability, to reduce the cost of maintenance, and to
prepare for functional enhancement. Object-oriented technology may be applied
as a means for improving maintainability and reducing costs.
• Migration: Old working software may still meet users’ needs, but it may be
based on hardware platforms, operating systems, or languages that have become
obsolete and thus may need to be re-engineered, transporting the software to a
newer platform or language. Migration may involve extensive redesign if the
new supporting platforms and operating systems are very different from the
original, such as the move from a mainframe to a network-based computing
environment.

4.19 SOFTWARE REENGINEERING LIFE CYCLE

In this section, we present an evolutionary view of the software reengineering life-
cycle:
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Requirements analysis phase: It refers to the identification of concrete reengineering Advanced Topics in
Software Engineering
goals for a given software. The specification of the criteria should be specified and
illustrated in the new reengineered system (for example, faster performance).
Violations that need to be repaired are also identified in this phase.
Model analysis phase: This refers to documenting and understanding the architecture
and the functionality of the legacy system being reengineered. In order to understand
and to transform a legacy system, it is necessary to capture its design, its architecture
and the relationships between different elements of its implementation. As a
consequence, a preliminary model is required in order to document the system and the
rationale behind its design. This requires reverse engineering the legacy system in
order to extract design information from its code.

Source code analysis phase: This phase refers to the identification of the parts of the
code that are responsible for violations of requirements originally specified in the
system’s analysis phase. This task encompasses the design of methods and tools to
inspect, measure, rank, and visualize software structures. Detecting error prone code
that deviates from its initial requirement specifications requires a way to measure
where and by how much these requirements are violated. Problem detection can be
based on a static analysis of the legacy system (i.e., analysing its source code or its
design structure), but it can also rely on a dynamic usage analysis of the system (i.e.,
an investigation of how programs behave at run-time).

Remediation phase: It refers to the selection of a target software structure that aims
to repair a design or a source code defect with respect to a target quality requirement.
Because legacy applications have been evolved in such a way that classes, objects,
and methods may heavily depend on each other, a detected problem may have to be
decomposed into simpler sub-problems.

Transformation phase: This consists of physically transforming software structures

according to the remediation strategies selected previously. This requires methods and
tools to manipulate and edit software systems, re-organise and re-compile them
automatically, debug and check their consistency, and manage different versions of
the software system being reengineered.

Evaluation phase refers to the process of assessing the new system as well as
establishing and integrating the revised system throughout the corporate operating
environment. This might involve the need for training and possibly the need for
adopting a new improved business process model.

Such a reengineering life-cycle yields a reengineering process. First, the source code
is represented as an Abstract Syntax Tree. The tree is further decorated with
annotations that provide linkage, scope, and type information. Once software artifacts
have been understood, classified and stored during the reverse engineering phase, their
behaviour can be readily available to the system during the forward engineering phase.
Then, the forward engineering phase aims to produce a new version of a legacy
system that operates on the target architecture and aims to address specific
maintainability or performance enhancements. Finally, we use an iterative procedure
to obtain the new migrant source code by selecting and applying a transformation
which leads to performance or maintainability enhancements. The transformation is
selected from the soft-goal interdependency graphs. The resulting migrant system is
then evaluated and the step is repeated until the specific quality requirements are met.

) Check Your Progress 4

1) What is Software Reengineering and what are its objectives?
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 Advanced Software 2) What is Reverse Engineering?
Engineering
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4.20 SUMMARY
In this unit, we have gone through the Formal Methods, Cleanroom software
engineering, Component Based Software Engineering and the Software
Reengineering process.
Formal methods promise to yield benefits in quality and productivity. They provide
an exciting paradigm for understanding software and its development, as well as a set
of techniques for use by software engineers. Formal methods can provide more
precise specifications, better internal communication, and an ability to verify designs
before executing them during test, higher quality and productivity. To get their full
advantages, formal methods should be incorporated into a software organisation’s
standard procedures. Software development is a social process, and the techniques
employed need to support that process. How to fully fit formal methods into the
lifecycle is not fully understood. Perhaps there is no universal answer, but only
solutions that vary from organisation to organisation.
Harlan Mills has developed the Cleanroom methodology, which is one approach for
integrating formal methods into the lifecycle. The Cleanroom approach combines
formal methods and structured programming with Statistical Process Control (SPC),
the spiral lifecycle and incremental releases, inspections, and software reliability
modeling. It fosters attitudes, such as emphasising defect prevention over defect
removal, that are associated with high quality products in non-software fields.
Component Based Software Engineering introduced major changes into design and
development practices, which introduces extra cost. Software engineers need to
employ new processes and ways of thinking – this, too, can introduce extra cost in
training and education. However, initial studies into the impact of CBSE on product
quality, development quality and cost, show an overall gain, and so it seems likely
that continuing these practices in the future will improve software development. It is
still not clear how exactly CBSE will mature, but it is clear that it aids in the
development of today’s large-scale systems, and will continue to aid in the
development of future systems, and is the perfect platform for addressing the
requirements of modern businesses.

Software reengineering is a very wide-ranging term that encompasses a great many

activities. As the name suggests, software reengineering is applied to existing pieces
of software, in an after-the-fact fashion, via the reapplication of an engineering
process.

4.21 SOLUTIONS / ANSWERS

Check Your Progress 1
1) Formal methods is that area of computer science that is concerned with the
application of mathematical techniques to the design and implementation of
computer software.
2) Following are the main parts to formal methods:
i) Formal specification: Using mathematics to specify the desired
properties of a computer system.
ii) Formal verification: Using mathematics to prove that a computer system
satisfies its specification.

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 iii) Automated programming: Automating the process of program Advanced Topics in
Software Engineering
generation.
Check Your Progress 2
1) The Cleanroom methodology is an iterative, life-cycle approach focused on
software quality, especially reliability. Begun by Harlan Mills, it combines
formal specifications, structured programming, formal verifications, formal
inspections, functional testing based on random selection of test data,
software reliability measurement, and Statistical Process Control (SPC) in an
integrated whole. The Cleanroom approach fosters attitudes, such as
emphasising defect prevention over defect removal, that are associated with
high quality products in fields other than software.
2) Statistical Process Control (SPC) is commonly used in manufacturing,
involves continuous process monitoring and improvement to reduce the
variance of outputs and to ensure that the process remains under control.
3) Benefits of Cleanroom software engineering include significant improvements
in correctness, reliability, and understandability. These benefits usually
translate into a reduction in field-experienced product failures, reduced cycle
time, ease of maintenance, and longer product life.
4) Cleanroom techniques are too theoretical, too mathematical, and too radical
for use in real software development. They rely on correctness verification
and statistical quality control rather than unit testing (a major departure from
traditional software development). Organisations operating at the ad hoc level
of the Capability Maturity Model do not make rigorous use of the defined
processes needed in all phases of the software life cycle.
Check Your Progress 3
1) Benefits of software reuse are:
• Increased Reliability: components already exercised in working systems
• Reduced Process Risk: Less uncertainty in development costs
• Effective Use of components: Reuse components instead of people
• Standards Compliance: Embed standards in reusable components
• Accelerated Development: Avoid custom development and speed up delivery.
2) COTS systems usually have a complete applications library and also offers an
applications programming interface (API). These are helpful in building large
systems by integrating COTS components is a viable development strategy for
some types of systems (e.g., E-commerce or video games).
Check Your Progress 4
1) Software reengineering is a process that aims to either
i) Improve understanding of a piece of software, or
ii) Prepare for an improvement in the software itself (e.g., increasing its
maintainability or reusability).
As the name suggests software reengineering is applied to existing pieces of software,
in an after-the-fact fashion, via the reapplication of an engineering process. Software
reengineering is a very wide-ranging term that encompasses a great many activities.
For example, software reengineering could involve refactoring a piece of software,
redocumenting it, reverse engineering it or changing its implementation language.
2) Reverse engineering is a process which is used to improve the understanding of
a program. So-called program comprehension is crucial to maintenance.
Approximately 50% of the development time of programmers is spent
understanding the code that they are working on. Reverse engineering often
involves the production of diagrams. It can be used to abstract away irrelevant

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 Advanced Software implementation and design details to recover the original requirements of the
Engineering
program.

4.22 FURTHER READINGS

1) Software Engineering, Sixth Edition, 2001, Ian Sommerville; Pearson
Education.

2) Software Engineering – A Practitioner’s Approach, Roger S. Pressman;

McGraw-Hill International Edition.

3) Component Software –Beyond Object-Oriented Programming,1998,

Szyperski C; Addison-Wesley.

4) Software Engineering, Schaum’s Outlines, 2003,David Gustafson,Tata

Mc Graw-Hill.
Reference websites
• http://www.rspa.com
• http://www.ieee.org

4.23 GLOSSARY
Software Reengineering: The examination and alteration of an existing subject
system to reconstitute it in a new form. This process encompasses a combination of
sub-processes such as reverse engineering, restructuring, redocumentation, forward
engineering, and retargeting.
Reverse Engineering: The engineering process of understanding, analysing, and
abstracting the system to a new form at a higher abstraction level.
Forward Engineering: Forward engineering is the set of engineering activities that
consume the products and artifacts derived from legacy software and new
requirements to produce a new target system.
Data Reengineering: Tools that perform all the reengineeering functions associated
with source code (reverse engineering, forward engineering, translation,
redocumentation, restructuring / normalisation, and retargeting) but act upon data
files.
Redocumentation: The process of analysing the system to produce support
documentation in various forms including users manuals and reformatting the
systems’ source code listings.
Restructuring: The engineering process of transforming the system from one
representation form to another at the same relative abstraction level, while preserving
the subject system’s external functional behavior.

Retargeting: The engineering process of transforming and hosting / porting the

existing system with a new configuration.

Source Code Translation: Transformation of source code from one language to

another or from one version of a language to another version of the same language
(e.g., going from COBOL-74 to COBOL-85).

Business Process Reengineering (BPR): The fundamental rethinking and radical

redesign of business processes to achieve dramatic improvements in critical,
contemporary measures of performance, such as cost, quality, service, and speed.

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