UNIT - I

INTRODUCTION:

Software Engineering is a framework for building software and is an engineering approach to

software development. Software programs can be developed without S/E principles and methodologies
but they are indispensable if we want to achieve good quality software in a cost effective manner.
Software is defined as:
Instructions + Data Structures + Documents

Engineering is the branch of science and technology concerned with the design, building, and use of
engines, machines, and structures . It is the application of science, tools and methods to find cost
effective solution to simple and complex problems.

SOFTWARE ENGINEERING is defined as a systematic, disciplined and quantifiable approach for the
development, operation and maintenance of software.

The Evolving role of software

The dual role of Software is as follows:
1. A Product- Information transformer producing, managing and displaying information.
2. A Vehicle for delivering a product- Control of computer(operating system),the communication
of information(networks) and the creation of other programs.

Characteristics of software
• Software is developed or engineered, but it is not manufactured in the classical sense.
• Software does not wear out, but it deteriorates due to change.
• Software is custom built rather than assembling existing components.

THE CHANGING NATURE OFSOFTWARE

The various categories of software are
1. System software
2. Application software
3. Engineering and scientific software
4. Embedded software
5. Product-line software
6. Web-applications
7. Artificial intelligence software

• System software. System software is a collection of programs written to service other programs
• Embedded software-- resides in read-only memory and is used to control products and systems
for the consumer and industrial markets.
• Artificial intelligence software. Artificial intelligence (AI) software makes use of nonnumeric
algorithms to solve complex problems that are not amenable to computation or straightforward
analysis
• Engineering and scientific software. Engineering and scientific software have been characterize

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by "number crunching" algorithms.

LEGACY SOFTWARE

Legacy software are older programs that are developed decades ago. The quality of legacy software is
poor because it has inextensible design, convoluted code, poor and nonexistent documentation, test
cases and results that are not achieved.
As time passes legacy systems evolve due to following reasons:
 The software must be adapted to meet the needs of new computing environment or technology.
 The software must be enhanced to implement new business requirements.
 The software must be extended to make it interoperable with more modern systems or database
 The software must be rearchitected to make it viable within a network environment.

SOFTWARE MYTHS
Myths are widely held but false beliefs and views which propagate misinformation and confusion.
Three types of myth are associated with software:
- Management myth
- Customer myth
- Practitioner’s myth

MANAGEMENT MYTHS
• Myth(1)-The available standards and procedures for software are enough.
• Myth(2)-Each organization feel that they have state-of-art software development tools since
they have latest computer.
• Myth(3)-Adding more programmers when the work is behind schedule can catch up.
• Myth(4)-Outsourcing the software project to third party, we can relax and let that party build it.

CUSTOMER MYTHS
• Myth(1)- General statement of objective is enough to begin writing programs, the details can
be filled in later.
• Myth(2)-Software is easy to change because software is flexible

PRACTITIONER’S MYTH
• Myth(1)-Once the program is written, the job has been done.
• Myth(2)-Until the program is running, there is no way of assessing the quality.
• Myth(3)-The only deliverable work product is the working program
• Myth(4)-Software Engineering creates voluminous and unnecessary documentation and
invariably slows down software development.

SOFTWARE ENGINEERING-A LAYERED TECHNOLOGY

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 Fig: Software Engineering-A layered technology

SOFTWARE ENGINEERING - A LAYERED TECHNOLOGY

• Quality focus - Bedrock that supports Software Engineering.
• Process - Foundation for software Engineering
• Methods - Provide technical How-to’s for building software
• Tools - Provide semi-automatic and automatic support to methods

A PROCESS FRAMEWORK
• Establishes the foundation for a complete software process
• Identifies a number of framework activities applicable to all software projects
• Also include a set of umbrella activities that are applicable across the entire software process.

A PROCESS FRAMEWORK comprises of :

Common process framework Umbrella activities Framework activities
Tasks, Milestones, deliverables SQA points

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 A PROCESS FRAMEWORK
Used as a basis for the description of process models Generic process activities
• Communication
• Planning
• Modeling
• Construction
• Deployment

A PROCESS FRAMEWORK
Generic view of engineering complimented by a number of umbrella activities
 Software project tracking and control
 Formal technical reviews
 Software quality assurance
 Software configuration management
 Document preparation and production
 Reusability management
 Measurement
 Risk management

CAPABILITY MATURITY MODEL INTEGRATION(CMMI)

• Developed by SEI(Software Engineering institute)
• Assess the process model followed by an organization and rate the organization with different levels
• A set of software engineering capabilities should be present as organizations reach different levels
of process capability and maturity.

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 CMMI process meta model can be represented in different ways
1.A continuous model
2.A staged model

Continuous model:
-Lets organization select specific improvement that best meet its business objectives and minimize
risk- Levels are called capability levels.
-Describes a process in 2 dimensions
-Each process area is assessed against specific goals and practices and is rated according to the
following capability levels.

CMMI
• Six levels of CMMI
– Level 0:Incomplete
– Level 1:Performed
– Level 2:Managed
– Level 3:Defined
– Level 4:Quantitatively managed
– Level 5:Optimized

CMMI
• Incomplete -Process is adhoc . Objective and goal of process areas are not known
• Performed -Goal, objective, work tasks, work products and other activities of software process
are carried out
• Managed -Activities are monitored, reviewed, evaluated and controlled
• Defined -Activities are standardized, integrated and documented
• Quantitatively Managed -Metrics and indicators are available to measure the process and quality
• Optimized - Continuous process improvement based on quantitative feed back from the user
-Use of innovative ideas and techniques, statistical quality control and other methods for
process improvement.

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 CMMI - Staged model
- This model is used if you have no clue of how to improve the process for quality software.
- It gives a suggestion of what things other organizations have found helpful to work first
- Levels are called maturity levels

PROCESS PATTERNS
Software Process is defined as collection of Patterns.Process pattern provides a template. It comprises of
• Process Template
-Pattern Name
-Intent
-Types
-Task pattern
- Stage pattern
-Phase Pattern
• Initial Context
• Problem
• Solution
• Resulting Context
• Related Patterns

PROCESS ASSESSMENT
Does not specify the quality of the software or whether the software will be
delivered on time or will it stand up to the user requirements. It attempts to keep a check on the current
state of the software process with the intention of improving it.
PROCESS ASSESSMENT
Software Process
Software Process Assessment Software Process improvement Motivates Capability determination
APPROACHES TO SOFTWARE ASSESSMENT
• Standard CMMI assessment (SCAMPI)
• CMM based appraisal for internal process improvement
• SPICE(ISO/IEC 15504)
• ISO 9001:2000 for software
Personal and Team Software
Process Personal software process
 PLANNING
 HIGH LEVEL DESIGN
 HIGH LEVEL DESIGN REVIEW
 DEVELOPMENT
 POSTMORTEM

Personal and Team Software Process

Team software process Goal of TSP
- Build self-directed teams
- Motivate the teams
- Acceptance of CMM level 5 behavior as normal to accelerate software process improvement
- Provide improvement guidance to high maturity organization

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 PROCESS MODELS

• Help in the software development

• Guide the software team through a set of framework activities
• Process Models may be linear, incremental or evolutionary

THE WATERFALL MODEL

• Used when requirements are well understood in the beginning

• Also called classic life cycle
• A systematic, sequential approach to Software development
• Begins with customer specification of Requirements and progresses through planning,
modeling, construction and deployment.

Communication
Planning
Modeling
Construction
Deployment

This Model suggests a systematic, sequential approach to SW development that begins at the
system level and progresses through analysis, design, code and testing

PROBLEMS IN WATERFALLMODEL
• Real projects rarely follow the sequential flow since they are always iterative
• The model requires requirements to be explicitly spelled out in the beginning, which is
often difficult
• A working model is not available until late in the project time plan

THE INCREMENTAL PROCESS MODEL

• Linear sequential model is not suited for projects which are iterative in nature
• Incremental model suits such projects
• Used when initial requirements are reasonably well-defined and compelling need to provide
limited functionality quickly
• Functionality expanded further in later releases
• Software is developed in
increments The Incremental Model
 Communication
 Planning
 Modeling
 Construction
 Deployment

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 INCREMENT 1

Communication
Planning
Modeling Construction
Deployment

INCREMENT 2

Communication
Planning
Modeling
Construction
: Deployment
:
:
:

INCREMENT N

Communication
Planning
Modeling
Construction
Deployment

THE INCREMENTAL MODEL

• Software releases in increments
• 1st increment constitutes Core product
• Basic requirements are addressed
• Core product undergoes detailed evaluation by the customer
• As a result, plan is developed for the next increment. Plan addresses the modification of
core product to better meet the needs of customer
• Process is repeated until the complete product is produced

THE RAD (Rapid Application Development) MODEL

• An incremental software process model

• Having a short development cycle
• High-speed adoption of the waterfall model using a component based construction approach
• Creates a fully functional system within a very short span time of 60 to 90 days

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 The RAD Model consists of the following phases:
Communication Planning Construction
Component reuses automatic code generation
testing Modeling
Business modeling Data modeling Process modeling
Deployment integration delivery feedback

THE RAD MODEL

• Multiple software teams work in parallel on different functions
• Modeling encompasses three major phases: Business modeling, Data modeling and
process modeling
• Construction uses reusable components, automatic code generation and testing

Problems in RAD
• Requires a number of RAD teams
• Requires commitment from both developer and customer for rapid-fire completion of activities
• Requires modularity
• Not suited when technical risks are high

EVOLUTIONARY PROCESSMODEL

• Software evolves over a period of time

• Business and product requirements often change as development proceeds making a straight-
line path to an end product unrealistic
• Evolutionary models are iterative and as such are applicable to modern day applications

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 Types of evolutionary models
– Prototyping
– Spiral model
– Concurrent development model

PROTOTYPING

• Mock up or model( throw away version) of a software product

• Used when customer defines a set of objective but does not identify input, output, or
processing requirements
• Developer is not sure of:
– efficiency of an algorithm
adaptability of an operating system
– human/machine interaction

Communication Quick Plan

Quick Design

Build Prototype Deployment & Delivery

STEPS IN PROTOTYPING
• Begins with requirement gathering
• Identify whatever requirements are known
• Outline areas where further definition is mandatory
• A quick design occur
• Quick design leads to the construction of prototype
• Prototype is evaluated by the customer

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 • Requirements are refined
• Prototype is turned to satisfy the needs of customer
LIMITATIONS OF PROTOTYPING
• In a rush to get it working, overall software quality or long term maintainability are
generally overlooked
• Use of inappropriate OS or PL
• Use of inefficient algorithm

THE SPIRAL MODEL

An evolutionary model which combines the best feature of the classical life cycle and
the iterative nature of prototype model. Include new element : Risk element. Starts in middle and
continually visits the basic tasks of communication, planning, modeling, construction and deployment

THE SPIRAL MODEL

• Realistic approach to the development of large scale system and software
• Software evolves as process progresses
• Better understanding between developer and customer
• The first circuit might result in the development of a product specification

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 • Subsequent circuits develop a prototype
• And sophisticated version of software

THE CONCURRENT DEVELOPMENT MODEL

• Also called concurrent engineering

• Constitutes a series of framework activities, software engineering action, tasks and their
associated states
• All activities exist concurrently but reside in different states
• Applicable to all types of software development
• Event generated at one point in the process trigger transitions among the states

A FINAL COMMENT ON EVOLUTIONARY PROCESS

• Difficult in project planning
• Speed of evolution is not known
Does not focus on flexibility and extensibility (more emphasis on high quality)
• Requirement is balance between high quality and flexibility and extensibility

THE UNIFIED PROCESS

Evolved by Rumbaugh, Booch, Jacobson. Combines the best features their OO models. Adopts
additional features proposed by other experts. Resulted in Unified Modeling Language (UML). Unified
process developed Rumbaugh and Booch. A framework for Object-Oriented Software
Engineering using UML

PHASES OF UNIFIED PROCESS

• INCEPTION PHASE
• ELABORATION PHASE
• CONSTRUCTION PHASE
• TRANSITION PHASE

The Unified Process (UP)

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 UNIFIED PROCESS WORK PRODUCTS
Tasks which are required to be completed during different phases
1. Inception Phase
*Vision document
*Initial Use-Case model
*Initial Risk assessment
*Project Plan

2. Elaboration Phase
*Use-Case model
*Analysis model
*Software Architecture description
*Preliminary design model
*Preliminary model

3. Construction Phase
*Design model
*System components
*Test plan and procedure
*Test cases
*Manual

4. Transition Phase
*Delivered software increment
*Beta test results
*General user feedback

Agility and Agile Process model

The meaning of Agile is swift or versatile."Agile process model" refers to a software

development approach based on iterative development. Agile methods break tasks into smaller
iterations, or parts
do not directly involve long term planning. The project scope and requirements are laid down at the
beginning of the development process. Plans regarding the number of iterations, the duration and the
scope of each iteration are clearly defined in advance

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 Phases of Agile model:
1. Requirements gathering
2.Design the requirements
3.Construction/ iteration
4.Testing/ Quality
assurance 5.Deployment
6. Feedback

1. Requirements gathering: In this phase, you must define the requirements. You
should explain business opportunities and plan the time and effort needed to build the
project. Based on this information, you can evaluate technical and economic
feasibility.

2. Design the requirements: When you have identified the project, work with stakeholders
to define requirements. You can use the user flow diagram or the high-level UML diagram
to show the work of new features and show how it will apply to your existing system.

3. Construction/ iteration: When the team defines the requirements, the work begins.
Designers and developers start working on their project, which aims to deploy a
working product. The product will undergo various stages of improvement, so it
includes simple, minimal functionality.

4. Testing: In this phase, the Quality Assurance team examines the product's performance
and looks for the bug.
5. Deployment: In this phase, the team issues a product for the user's work environment.
6. Feedback: After releasing the product, the last step is feedback. In this, the team
receives feedback about the product and works through the feedback.
Advantages:

1. Frequent Delivery
2. Face-to-Face Communication with clients.
3.Efficient design and fulfils the business
requirement.
4. Anytime changes are acceptable.
5. It reduces total development time.

Disadvantages:

1. Due to the shortage of formal documents, it

creates confusion and crucial decisions
taken throughout various phases can be misinterpreted at any time by different team
members.

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 2. Due to the lack of proper documentation, once the project completes and the
developers allotted to another project, maintenance of the finished project can become a
difficulty.

Extreme Programming
XP is a lightweight, efficient, low-risk, flexible, predictable, scientific, and fun way to develop
software.
Extreme Programming (XP) was conceived and developed to address the specific needs of
software development by small teams in the face of vague and changing requirements.
Extreme Programming is one of the Agile software development methodologies. It provides
values and principles to guide the team behavior. The team is expected to self-organize.
Extreme Programming provides specific core practices where −
 Each practice is simple and self-complete.
 Combination of practices produces more complex and emergent behaviour.

Other process models of Agile Development and Tools

 Crystal
 Scrum
Scrum
Scrum is aimed at sustaining strong collaboration between people working on complex
products, and details are being changed or added. It is based upon the systematic interactions
between the three major roles: Scrum Master, Product Owner, and the Team.

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  Scrum Master is a central figure within a project. His principal responsibility is to
eliminate all the obstacles that might prevent the team from working efficiently.
 Product Owner, usually a customer or other stakeholder, is actively involved throughout
the project, conveying the global vision of the product and providing timely feedback on the
job done after every sprint.
 Scrum Team is a cross-functional and self-organizing group of people that is responsible
for the product implementation. It should consist of up to 7 team members, in order to stay
flexible and productive.

Crystal
Crystal is an agile methodology for software development. It places focus on people over
processes, to empower teams to find their own solutions for each project rather than being
constricted with rigid methodologies.
Crystal methods focus on:-
People involved
Interaction between the
teams Community
Skills of people
involved Their Talents
Communication between all the teams

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 MALLA REDDY COLLEGE OF ENGINEERING &
TECHNOLOGY DEPARTMENTOF COMPUTER SCIENCE AND
ENGINEERING

UNIT II
SOFTWARE
REQUIREMENTS

IEEE defines Requirement as :

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 or a system component
to satisfy constract, standard, specification or formally imposed document
3. A documented representation of a condition nor capability as in 1 or 2

SOFTWARE REQUIREMENTS
• Encompasses both the User’s view of the requirements( the external view ) and the
Developer’s view( inside characteristics)
User’s Requirements
--Statements in a natural language plus diagram, describing the services the system is expected to
provide and the constraints
• System Requirements --Describe the system’s function, services and operational condition

SOFTWARE REQUIREMENTS
• System Functional Requirements
--Statement of services the system should provide
--Describe the behavior in particular situations
--Defines the system reaction to particular inputs
• Nonfunctional Requirements
- Constraints on the services or functions offered by the system
--Include timing constraints, constraints on the development process and standards
--Apply to system as a whole
• Domain Requirements
--Requirements relate to specific application of the system
--Reflect characteristics and constraints of that system

FUNCTIONAL REQUIREMENTS
• Should be both complete and consistent
• Completeness
-- All services required by the user should be defined
• Consistent
-- Requirements should not have contradictory definition
• Difficult to achieve completeness and consistency for large system

NON-FUNCTIONALREQUIREMENTS
Types of Non-functional Requirements 1.Product Requirements
-Specify product behavior
-Include the following

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 • Usability
• Efficiency
• Reliability
• Portability
2. Organizational Requirements
--Derived from policies and procedures
--Include the following:
• Delivery
• Implementation
• Standard
3. External Requirements
-- Derived from factors external to the system and its development process
--Includes the following
• Interoperability
• Ethical
• Legislative
PROBLEMS FACED USING THE NATURAL LANGUAGE
1. Lack of clarity-- Leads to misunderstanding because of ambiguity of natural language
2. Confusion-- Due to over flexibility, sometime difficult to find whether requirements are same or
distinct.
3. Amalgamation problem-- Difficult to modularize natural language requirements

STRUCTURED LANGUAGESPECIFICATION
• Requirements are written in a standard way
• Ensures degree of uniformity
• Provide templates to specify system requirements
• Include control constructs and graphical highlighting to partition the specification

SYSTEM REQUIREMENTS STANDARD FORM

• Function
• Description
• Inputs
• Source
• Outputs
• Destination
• Action
• Precondition
• Post condition
• Side effects

Interface Specification
• Working of new system must match with the existing system
• Interface provides this capability and precisely specified

Three types of interfaces

1. Procedural interface-- Used for calling the existing programs by the new programs 2.Data structures-
-Provide data passing from one sub-system to another 3.Representations of Data
-- Ordering of bits to match with the existing system
--Most common in real-time and embedded system

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 The Software Requirements document
The requirements document is the official statement of what is required of the system developers.
Should include both a definition of user requirements and a specification of the system requirements. It
is NOT a design document. As far as possible, it should set of WHAT the system should do rather than
HOW it should do it

The Software Requirements document

Suggests that there are 6 requirements that requirement document should satisfy. It should
• specify only external system behavior
• Specify constraints on the implementation.
• Be easy to change
• Serve as reference tool for system maintainers
• Record forethought about the life cycle of the system.
• Characterize acceptable responses to undesired events

Purpose of SRS
• Communication between the Customer, Analyst, system developers, maintainers,
• firm foundation for the design phase
• support system testing activities
• Support project management and control
• controlling the evolution of the system

IEEE requirements standard

Defines a generic structure for a requirements document that must be instantiated for each specific
system.
– Introduction.
– General description.
– Specific requirements.
– Appendices.
– Index.

IEEE requirements standard

1.Introduction Purpose
Scope
Definitions, Acronyms and
Abbreviations References
Overview
2. General description
Product perspective
Product function
summary User
characteristics General
constraints
Assumptions and dependencies
3. Specific Requirements
- Functional requirements

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 -External interface requirements
- Performance requirements
- Design constraints
- Attributes eg. security, availability, maintainability, transferability/conversion
- Other requirements
• Appendices
• Index
REQUIREMENTS ENGINEERING PROCESS
To create and maintain a system requirement document. The overall process includes four high level
requirements engineering sub-processes:
1. Feasibility study
--Concerned with assessing whether the system is useful to the business 2.Elicitation and analysis
--Discovering requirements 3.Specifications
--Converting the requirements into a standard form 4.Validation
-- Checking that the requirements actually define the system that the customer wants

SPIRAL REPRESENTATION OF REQUIREMENTSENGINEERING PROCESS

Process represented as three stage activity. Activities are organized as an iterative process around a
spiral. Early in the process, most effort will be spent on understanding high-level business and the use
requirement. Later in the outer rings, more effort will be devoted to system requirements engineering
and system modeling
Three level process consists of: 1.Requirements elicitation
2. Requirements specification
3. Requirements validation

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 FEASIBILITY STUDIES
Starting point of the requirements engineering process
• Input: Set of preliminary business requirements, an outline description of the system and how
the system is intended to support business processes
• Output: Feasibility report that recommends whether or not it is worth carrying out further
Feasibility report answers a number of questions:
1. Does the system contribute to the overall objective
2. Can the system be implemented using the current technology and within given cost and schedule
3. Can the system be integrated with other system which are already in place.

REQUIREMENTS ELICITATION ANALYSIS

Involves a number of people in an organization.

Stakeholder definition-- Refers to any person or group who will be affected by the system directly
or indirectly i.e. End-users, Engineers, business managers, domain experts.

Reasons why eliciting is difficult

1. Stakeholder often don’t know what they want from the computer system. 2. Stakeholder expression of
requirements in natural language is sometimes difficult toUnderstand.
3. Different stakeholders express requirements differently
4. Influences of political factors Change in requirements due to dynamic environments.

REQUIREMENTS ELICITATION PROCESS

Process activities
1. Requirement Discovery -- Interaction with stakeholder to collect their requirements
including domain and documentation
2. Requirements classification and organization -- Coherent clustering of requirements
from unstructured collection of requirements
3. Requirements prioritization and negotiation -- Assigning priority to requirements
--Resolves conflicting requirements through negotiation
4. Requirements documentation -- Requirements be documented and placed in the next round of spiral

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 The spiral representation of Requirements Engineering

REQUIEMENTS DICOVERY TECHNIQUES

1. View points --Based on the viewpoints expressed by the stake holder

--Recognizes multiple perspectives and provides a framework for discovering conflicts in the
requirements proposed by different stakeholders
Three Generic types of viewpoints
1. Interactor viewpoint--Represents people or other system that interact directly with the system
2. Indirect viewpoint--Stakeholders who influence the requirements, but don’t use the system
3.Domain viewpoint--Requirements domain characteristics and constraints that influence the
requirements.

2. Interviewing--Puts questions to stakeholders about the system that they use and the system to
be developed. Requirements are derived from the answers.
Two types of interview
– Closed interviews where the stakeholders answer a pre-defined set of questions.
– Open interviews discuss a range of issues with the stakeholders for better understanding their needs.

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 Effective interviewers
a) Open-minded: no pre-conceived ideas
b) Prompter: prompt the interviewee to start discussion with a question or a proposal

3. Scenarios --Easier to relate to real life examples than to abstract description. Starts with an outline
of the interaction and during elicitation, details are added to create a complete description of that
interaction
Scenario includes:
• 1. Description at the start of the scenario
• 2. Description of normal flow of the event
• 3. Description of what can go wrong and how this is handled
• 4.Information about other activities parallel to the scenario
• 5.Description of the system state when the scenario finishes

LIBSYS scenario
• Initial assumption: The user has logged on to the LIBSYS system and has located the
journal containing the copy of the article.
• Normal: The user selects the article to be copied. He or she is then prompted by the system to
either provide subscriber information for the journal or to indicate how they will pay for the article.
Alternative payment methods are by credit card or by quoting an organizational account number.
• The user is then asked to fill in a copyright form that maintains details of the transaction and
they then submit this to the LIBSYS system.
• The copyright form is checked and, if OK, the PDF version of the article is downloaded to the
LIBSYS working area on the user’s computer and the user is informed that it is available. The user
is asked to select a printer and a copy of the article is printed

LIBSYS scenario
• What can go wrong: The user may fail to fill in the copyright form correctly. In this case, the
form should be re-presented to the user for correction. If the resubmitted form is still incorrect then
the user’s request for the article is rejected.
• The payment may be rejected by the system. The user’s request for the article is rejected.
• The article download may fail. Retry until successful or the user terminates the session..
• Other activities: Simultaneous downloads of other articles.
• System state on completion: User is logged on. The downloaded article has been deleted
from LIBSYS workspace if it has been flagged as print-only.

4. Use cases -- scenario based technique for requirement elicitation. A fundamental feature of
UML, notation for describing object-oriented system models. Identifies a type of interaction and the
actors involved. Sequence diagrams are used to add information to a Use case

Article printing use-case Article printing

LIBSYS use cases Article printing Article

search
User administration Supplier Catalogue services Library

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 User Library Staff

REQUIREMENTS VALIDATION
Concerned with showing that the requirements define the system that the customer wants.
Important because errors in requirements can lead to extensive rework cost
Validation checks
1. Validity checks --Verification that the system performs the intended function by the user 2.Consistency
check --Requirements should not conflict
3. Completeness checks --Includes requirements which define all functions and constraints
intended bythe system user
4. Realism checks --Ensures that the requirements can be actually implemented
5. Verifiability -- Testable to avoid disputes between customer and developer.

VALIDATION TECHNIQUES 1.REQUIREMENTS REVIEWS

Reviewers check the following:
(a) Verifiability: Testable
(b) Comprehensibility
(c) Traceability
(d) Adaptability 2.PROTOTYPING

3. TEST-CASE

GENERATION Requirements

management
Requirements are likely to change for large software systems and as such requirements
management process is required to handle changes.
Reasons for requirements changes
(a) Diverse Users community where users have different requirements and priorities
(b) System customers and end users are different
(c) Change in the business and technical environment after installation Two classes of requirements
(a) Enduring requirements: Relatively stable requirements
(b) Volatile requirements: Likely to change during system development process or during operation

Requirements management planning

An essential first stage in requirement management process. Planning process consists of the following
1. Requirements identification -- Each requirement must have unique tag for cross reference
and traceability
2. Change management process -- Set of activities that assess the impact and cost of changes
3.Traceability policy -- A matrix showing links between requirements and other elements of software
development
4. CASE tool support --Automatic tool to improve efficiency of change management process.
Automatedtools are required for requirements storage, change management and traceability
management

Traceability
Maintains three types of traceability information.
1. Source traceability--Links the requirements to the stakeholders
2. Requirements traceability--Links dependent requirements within the requirements document
3. Design traceability-- Links from the requirements to the design module

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 A traceability matrix Requirements change management
consists of three principal stages:
1. Problem analysis and change specification-- Process starts with a specific change proposal
and analysed to verify that it is valid
2. Change analysis and costing--Impact analysis in terms of cost, time and risks
3. Change implementation--Carrying out the changes in requirements document, system design and
its implementation

SYSTEM MODELS
Used in analysis process to develop understanding of the existing system or new system. Excludes
details. An abstraction of the system
Types of system models 1.Context models
2. Behavioural models 3.Data models 4.Object models 5.Structured models

CONTEXT MODELS
A type of architectural model. Consists of sub-systems that make up an entire system First step: To
identify the subsystem.
Represent the high level architectural model as simple block diagram
• Depict each sub system a named rectangle
• Lines between rectangles indicate associations between subsystems Disadvantages
--Concerned with system environment only, doesn't take into account other systems, which may
take data or give data to the model

The context of an ATM system consists of the following Auto-teller

system Security system Maintenance system Account data base Usage
database Branch accounting system Branch counter system

Behavioral models
Describes the overall behaviour of a system. Two types of behavioural
model 1.Data Flow models 2.State machine models

Data flow models --Concentrate on the flow of data and functional transformation on that data. Show the
processing of data and its flow through a sequence of processing steps. Help analyst understand what is
going on

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 Advantages
-- Simple and easily understandable
-- Useful during analysis of requirements

State machine models

Describe how a system responds to internal or external events. Shows system states and events that
cause transition from one state to another. Does not show the flow of data within the system. Used for
modeling of real time systems
Exp: Microwave oven
Assumes that at any time, the system is in one of a number of possible states. Stimulus triggers a
transition from on state to another state
Disadvantage
-- Number of possible states increases rapidly for large system models

DATA MODELS
Used to describe the logical structure of data processed by the system. An entity-relation- attribute
model sets out the entities in the system, the relationships between these entities and the entity
attributes. Widely used in database design. Can readily be implemented using relational databases. No
specific notation provided in the UML but objects and associations can be used.

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 Library semantic model

Data dictionary entries

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 OBJECT MODELS
An object oriented approach is commonly used for interactive systems development. Expresses the
systems requirements using objects and developing the system in an object oriented PL such as c++
A object class: An abstraction over a set of objects that identifies common attributes. Objects are
instances of object class. Many objects may be created from a single class.
Analysis process
-- Identifies objects and object classes Object class in UML
--Represented as a vertically oriented rectangle with three sections
(a) The name of the object class in the top section
(b) The class attributes in the middle section
(c) The operations associated with the object class are in lower section.

OBJECT MODELS INHERITANCE MODELS

A type of object oriented model which involves in object classes attributes. Arranges classes into
an inheritance hierarchy with the most general object class at the top of hierarchy Specialized
objects inherit their attributes and services
UML notation
-- Inheritance is shown upward rather than downward
--Single Inheritance: Every object class inherits its attributes and operations from a single parent class
--Multiple Inheritance: A class of several of several parents.

OBJECT MODELS OBJECT AGGREGATION

Some objects are grouping of other objects. An aggregate of a set of other objects. The classes
representing these objects may be modeled using an object aggregation model A diamond shape on the
source of the link represents the composition.

OBJECT-BEHAVIORAL MODEL
-- Shows the operations provided by the objects
-- Sequence diagram of UML can be used for behavioral modeling

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 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
DEPARTMENTOF COMPUTER SCIENCE AND ENGINEERING

UNIT III

DESIGN ENGINEERING

DESIGN PROCESS AND DESIGN QUALITY

Encompasses the set of principles, concepts and practices that lead to the development of high
quality system or product. Design creates a representation or model of the software. Design model
provides details about S/W architecture, interfaces and components that are necessary to implement the
system. Quality is established during Design. Design should exhibit firmness, commodity and design.
Design sits at the kernel of S/W Engineering. Design sets the stage for construction.

QUALITY GUIDELINES
• Uses recognizable architectural styles or patterns
• Modular; that is logically partitioned into elements or subsystems
• Distinct representation of data, architecture, interfaces and components
• Appropriate data structures for the classes to be implemented
• Independent functional characteristics for components
• Interfaces that reduces complexity of connection
• Repeatable method

QUALITY ATTRIBUTES
FURPS quality attributes
• Functionality
* Feature set and capabilities of programs
* Security of the overall system
• Usability
* user-friendliness
* Aesthetics
* Consistency
* Documentation
• Reliability
* Evaluated by measuring the frequency and severity of failure
* MTTF
• Supportability
* Extensibility
* Adaptability
* Serviceability

DESIGN CONCEPTS
1. Abstractions
2. Architecture
3. Patterns
4. Modularity
5. Information Hiding

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 6. Functional Independence
7. Refinement
8. Re-factoring
9. Design Classes

DESIGN CONCEPTS
ABSTRACTION
Many levels of abstraction.
Highest level of abstraction: Solution is slated in broad terms using the language of the
problem environment
Lower levels of abstraction: More detailed description of the solution is provided
• Procedural abstraction-- Refers to a sequence of instructions that a specific and limited function
• Data abstraction-- Named collection of data that describe a data object

DESIGN CONCEPTS
ARCHITECTURE--Structure organization of program components (modules) and their interconnection
Architecture Models
(a) Structural Models-- An organized collection of program components
(b) Framework Models-- Represents the design in more abstract way
(c) Dynamic Models-- Represents the behavioral aspects indicating changes as a function of
external events
(d). Process Models-- Focus on the design of the business or technical process

PATTERNS
Provides a description to enables a designer to determine the followings: (a). whether the pattern
isapplicable to the current work
(b). Whether the pattern can be reused
(c). Whether the pattern can serve as a guide for developing a similar but functionally or
structurally different pattern

MODULARITY
Divides software into separately named and addressable components, sometimes called
modules. Modules are integrated to satisfy problem requirements. Consider two problems p1
and p2. If the complexity of p1 iscp1 and of p2 is cp2 then effort to solve p1=cp1 and effort to
solve p2=cp2 If cp1>cp2 then ep1>ep2
The complexity of two problems when they are combined is often greater than the sum of the
perceived complexity when each is taken separately. • Based on Divide and Conquer strategy
: it is easier to solve a complex problem when broken into sub-modules

INFORMATION HIDING
Information contained within a module is inaccessible to other modules who do not need such
information. Achieved by defining a set of Independent modules that communicate with one another
only that information necessary to achieve S/W function. Provides the greatest benefits when
modifications are required during testing and later. Errors introduced during modification are less likely
to propagate to other location within the S/W.

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 FUNCTIONAL INDEPENDENCE
A direct outgrowth of Modularity. abstraction and information hiding. Achieved by developing a
module with single minded function and an aversion to excessive interaction with other modules. Easier
to develop and have simple interface. Easier to maintain because secondary effects caused b design or
code modification are limited, error propagation is reduced and reusable modules are possible.
Independence is assessed by two quantitative criteria:
(1) Cohesion
(2) Coupling
Cohesion -- Performs a single task requiring little interaction with other components Coupling--
Measure of interconnection among modules. Coupling should be low and cohesion should be high for
good design.

REFINEMENT & REFACTORING

REFINEMENT -- Process of elaboration from high level abstraction to the lowest level abstraction.
High level abstraction begins with a statement of functions. Refinement causes the designer to
elaborate providing more and more details at successive level of abstractions Abstraction and
refinement are complementary concepts.
Refactoring -- Organization technique that simplifies the design of a component without changing its
function or behavior. Examines for redundancy, unused design elements and inefficient or unnecessary
algorithms.

DESIGN CLASSES
Class represents a different layer of design architecture. Five types of Design Classes
1. User interface class -- Defines all abstractions that are necessary for human computer interaction
2. Business domain class -- Refinement of the analysis classes that identity attributes and services
to implement some of business domain
3. Process class -- implements lower level business abstractions required to fully manage the
business domain classes
4. Persistent class -- Represent data stores that will persist beyond the execution of the software
5. System class -- Implements management and control functions to operate and communicate
within the computer environment and with the outside world.

THE DESIGN MODEL

Analysis viewed in two different dimensions as process dimension and abstract dimension. Process
dimension indicates the evolution of the design model as design tasks are executed as part of software
process. Abstraction dimension represents the level of details as each element of the analysis model is
transformed into design equivalent
Data Design elements
-- Data design creates a model of data that is represented at a high level of abstraction
-- Refined progressively to more implementation-specific representation for processing by the computer
base system
-- Translation of data model into a data base is pivotal to achieving business objective of a system

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 THE DESIGN MODEL
Architectural design elements. Derived from three sources
(1) Information about the application domain of the software
(2) Analysis model such as dataflow diagrams or analysis classes.
(3) Architectural pattern and styles Interface Design elements Set of detailed drawings constituting:
(1) User interface
(2) External interfaces to other systems, devices etc
(3) Internal interfaces between various components

THE DESIGN MODEL

Deployment level design elements. Indicates how software functionality and subsystem will be allocated
within the physical computing environment. UML deployment diagram is developed and refined
Component level design elements Fully describe the internal details of each software component. UML
diagram can be used

CREATING AN ARCHITECTURAL DESIGN

What is SOFTWARE ARCHITECTURE… The software architecture of a program or computing
system is the structure or structures of the system, which comprise software components, the
externally visible properties of those components and the relationship among them.

Software Architecture is not the operational software. It is a representation that enables a software
engineer to
• Analyze the effectiveness of the design in meeting its stated requirements.
• • consider architectural alternative at a stage when making design changes is still relatively easy .
• Reduces the risk associated with the construction of the software.

Why Is Architecture Important? Three key reasons

--Representations of software architecture enable communication and understanding
between stakeholders
--Highlights early design decisions to create an operational entity.
--constitutes a model of software components and their interconnection

Data Design
The data design action translates data objects defined as part of the analysis model into data structures at
the component level and database architecture at application level when necessary.

DATA DESIGN AT ARCHITECTURE LEVEL

• Data structure at programming level
• Data base at application level
• Data warehouse at business level.

DATA DESIGN AT COMPONENT LEVEL

Principles for data specification:
1. Proper selection of data objects and data and data models

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 2. Identification of attribute and functions and their encapsulation of these within a class
3.Mechanism for representation of the content of each data object. Class diagrams may be used
4. Refinement of data design elements from requirement analysis to component level design.
5.Information hiding
6. A library of useful data structures and operations be developed.
7. Software design and PL should support the specification and realization of abstract data types..

ARCHITECTURAL STYLES
Describes a system category that encompasses:
(1) a set of components
(2) a set of connectors that enables “communication and coordination
(3) Constraints that define how components can be integrated to form the system
(4) Semantic models to understand the overall properties of a system

Data-flow architectures
Shows the flow of input data, its computational components and output data. Structure is also called
pipe and Filter. Pipe provides path for flow of data. Filters manipulate data and work independent of its
neighboring filter. If data flow degenerates into a single line of transform, it is termed as batch
sequential.
Call and return architectures
Achieves a structure that is easy to modify and scale .Two sub styles
(1) Main program/sub program architecture
-- Classic program structure

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 -- Main program invokes a number of components, which in turn invoke still other components

(2) Remote procedure call architecture

-- Components of main program/subprogram are distributed across computers over network
Object-oriented architectures
The components of a system encapsulate data and the operations. Communication and coordination
between components is done via message

Layered architectures
A number of different layers are defined Inner Layer( interface with OS)
• Intermediate Layer Utility services and application function) Outer Layer (User interface)

FIG: Layered

ARCHITECTURAL PATTERNS
A template that specifies approach for some behavioral characteristics of the system Patterns are
imposed on the architectural styles
Pattern Domains 1.Concurrency
--Handles multiple tasks that simulate parallelism.
--Approaches (Patterns)
(a) Operating system process management pattern
(b) A task scheduler pattern 2.Persistence
--Data survives past the execution of the process
--Approaches (Patterns)
(a) Data base management system pattern
(b) Application Level persistence Pattern( word processing software)

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 3. Distribution
-- Addresses the communication of system in a distributed environment
--Approaches (Patterns)
(a) Broker Pattern
-- Acts as middleman between client and server.

Object-Oriented Design: Objects and object classes, An Object-Oriented design process, Design
evolution.
• Performing User interface design: Golden rules, User interface analysis and design,
interface analysis, interface design steps, Design evaluation.

Object and Object Classes

• Object: An object is an entity that has a state and a defined set of operations that operate on
that state.
• An object class definition is both a type specification and a template for creating objects.
• It includes declaration of all the attributes and operations that are associated with object of that class.

Object Oriented Design Process

There are five stages of object oriented design process
1) Understand and define the context and the modes of use of the system. 2) Design the system
architecture
3) Identify the principle objects in the system. 4) Develop a design models
5)Specify the object interfaces

Systems context and modes of use. It specifies the context of the system. it also specify
the relationships between the software that is being designed and its external
environment.
• If the system context is a static model it describes the other system in that environment.
• If the system context is a dynamic model then it describes how the system actually interact
with theenvironment.

System Architecture
Once the interaction between the software system that being designed and the system environment have
been defined. We can use the above information as basis for designing the System

Architecture.

Object Identification--This process is actually concerned with identifying the object classes. We
can identify the object classes by the following
1) Use a grammatical analysis 2) Use a tangible entities 3) Use a behavioral approach
4) Use a scenario based approach

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 Design model
Design models are the bridge between the requirements and implementation. There are two type of
design models
1) Static model describe the relationship between the objects. 2) Dynamic model describe the
interaction between the objects

Object Interface Specification

It is concerned with specifying the details of the interfaces to objects.
Design evolution. The main advantage OOD approach is to simplify the problem of making changes to
the design. Changing the internal details of an object is unlikely to effect any other system object.

Golden Rules
1. Place the user in control
2. Reduce the user’s memory load
3. Make the interface consistent

Place the User in Control

• Define interaction modes in a way that does not force a user into unnecessary or undesired actions.
• Provide for flexible interaction.
• Allow user interaction to be interruptible and undoable.
• Streamline interaction as skill levels advance and allow the interaction to be customized.
• Hide technical internals from the casual user.
• Design for direct interaction with objects that appear on the screen.

Make the Interface Consistent. Allow the user to put the current task into a meaningful context.
Maintain consistency across a family of applications. If past interactive models have created user
expectations, do not make changes unless there is a compelling reason to do
so.

USER INTERFACE ANALYSISAND DESIGN

The overall process for analyzing and designing a user interface begins with the creation of different
models of system function. There are 4 different models that is to be considered when a user interface is
to be analyzed and designed.

User Interface Design Models

User model —Establishes a profile of all end users of the system
Design model — A design model of the entire system incorporates data, architectural, interface and
procedural representation of the software.
A design realization of the user model
User’s Mental model (system perception). the user’s mental image of what the interface is
Implementation model — the interface “look and feel” coupled with supporting information
that describe interface syntax and semantics

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 Users can be categorized as
1. Novice – No syntactic knowledge of the system and little semantic knowledge of the application
or computer usage of the system
2. Knowledgeable, intermittent users- Reasonable semantic knowledge of the application but
low recallof syntactic information to use the system
3. Knowledgeable, frequent users- Good semantic and syntactic knowledge

User interface analysis and design process

• The user interface analysis and design process is an iterative process and it can be represented as
a spiral model
It consists of 5 framework activities 1.User, task and environment analysis 2.Interface
design3.Interface construction 4.Interface validation

User Interface Design Process

Interface analysis
-Understanding the user who interacts with the system based on their skill levels.i.e, requirement
gathering
-The task the user performs to accomplish the goals of the system are identified, described and
elaborated. Analysis of work environment.

Interface design
In interface design, all interface objects and actions that enable a user to perform all desired task
are defined
Implementation
A prototype is initially constructed and then later user interface development tools may be used to
complete the construction of the interface.
• Validation
The correctness of the system is validated against the user requirement

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 Interface Analysis
Interface analysis means understanding
– (1) the people (end-users) who will interact with the system through the interface;
– (2) the tasks that end-users must perform to do their work,
– (3) the content that is presented as part of the interface
– (4) the environment in which these tasks will be conducted.

User Analysis
• Are users trained professionals, technician, clerical, o manufacturing workers?
• What level of formal education does the average user have?
• Are the users capable of learning from written materials or have they expressed a desire
for classroom training?
• Are users expert typists or keyboard phobic?
• What is the age range of the user community?
• Will the users be represented predominately by one gender?
• How are users compensated for the work they perform?
• Do users work normal office hours or do they work until the job is done?

Task Analysis and Modeling

Analysis Techniques
• Use-cases define basic interaction
• Task elaboration refines interactive tasks
• Object elaboration identifies interface objects(classes)
• Workflow analysis defines how a work process is completed when several people (and roles)
are involved
– What work will the user perform in specific circumstances?

Interface Design Steps

• Using information developed during interface analysis define interface objects and
actions (operations).
• Define events (user actions) that will cause the state of the user interface to change. Model
this behavior.
• Depict each interface state as it will actually look to the end-user.
• Indicate how the user interprets the state of the system from information provided through
the interface.

Interface Design Patterns. Patterns are available for

– The complete UI
– Page layout
– Forms and input
– Tables
– Direct data manipulation
– Navigation
– Searching
– Page elements
– e-Commerce

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 Design Issues
• Response time
• Help facilities
• Error handling
• Menu and command labeling
• Application accessibility
• Internationalization

Design Evaluation Cycle: Steps:

Preliminary design Build prototype #1

Interface evaluation is studied by designer Design modifications are made
Build prototype # n
Interface
User evaluate's interface Interface design is complete

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 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
DEPARTMENTOF COMPUTER SCIENCE AND ENGINEERING
UNIT IV

Testing Strategies: A strategic approach to software testing, test strategies for

conventional software, Black-Box and White-Box testing, Validation testing, System
testing, the art of Debugging.
Product metrics: Software Quality, Metrics for Analysis Model, Metrics for Design
Model, Metrics for source code, Metrics for testing, Metrics for maintenance.
Metrics for Process and Products: Software Measurement, Metrics for software quality.

Testing Strategies

Software is tested to uncover errors introduced during design and construction. Testing
often accounts for
More project effort than other s/e activity. Hence it has to be done carefully using a testing
strategy.
The strategy is developed by the project manager, software engineers and testing
specialists. Testing is the process of execution of a program with the intention of finding
errors Involves 40% of total project cost
Testing Strategy provides a road map that describes the steps to be conducted as part of
testing.
It should incorporate test planning, test case design, test execution and resultant data
collection and execution
Validation refers to a different set of activities that ensures that the software is traceable to
the Customer requirements.
V&V encompasses a wide array of Software Quality Assurance

A strategic Approach for Software testing

Testing is a set of activities that can be planned in advance and conducted systematically.
Testing strategy
Should have the following characteristics:
-- usage of Formal Technical reviews(FTR)
-- Begins at component level and covers entire system
-- Different techniques at different points
-- conducted by developer and test group
-- should include debugging
Software testing is one element of verification and validation.
Verification refers to the set of activities that ensure that software correctly implements
a specific function.
( Ex: Are we building the product right? )
Validation refers to the set of activities that ensure that the software built is traceable to
customer requirements.
( Ex: Are we building the right product ? )
Testing Strategy

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 Testing can be done by software developer and independent testing group. Testing
and debugging are different activities. Debugging follows testing
Low level tests verifies small code segments. High level tests validate major
system functions against customer requirements
Test Strategies for Conventional Software:
Testing Strategies for Conventional Software can be viewed as a spiral consisting of four
levels of testing:
1) Unit Testing
2)Integration Testing
3)Validation Testing
and
4) System Testing

Spiral Representation of Testing for Conventional Software

Unit Testing begins at the vortex of the spiral and concentrates on each unit of software
in source code.
It uses testing techniques that exercise specific paths in a component and its control structure to
ensure complete coverage and maximum error detection. It focuses on the internal processing logic
and data structures. Test cases should uncover errors.

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 Fig: Unit Testing

Boundary testing also should be done as s/w usually fails at its boundaries. Unit
tests can be designed before coding begins or after source code is generated.

Integration testing: In this the focus is on design and construction of the software architecture.
It addresses the issues associated with problems of verification and program construction by
testing inputs and outputs. Though modules function independently problems may arise
because of interfacing. This technique uncovers errors associated with interfacing. We can use
top-down integration wherein modules are integrated by moving downward through the control
hierarchy, beginning with the main control module. The other strategy is bottom –up which
begins construction and testing with atomic modules which are combined into clusters as we
move up the hierarchy. A combined approach called Sandwich strategy can be used i.e., top-
down for higher level modules and bottom-up for lower level modules.

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 Validation Testing: Through Validation testing requirements are validated against s/w
constructed. These are high-order tests where validation criteria must be evaluated to
assure that s/w meets all functional, behavioural and performance requirements. It
succeeds when the software functionsin a manner that can be reasonably expected by
the customer.
1)Validation Test
Criteria 2)Configuration
Review 3)Alpha And
Beta Testing
The validation criteria described in SRS form the basis for this testing. Here, Alpha and Beta
testing is performed. Alpha testing is performed at the developers site by end users in a natural
setting and with a controlled environment. Beta testing is conducted at end-user sites. It is a
“live” application and environment is not controlled.
End-user records all problems and reports to developer. Developer then makes modifications
and releases the product.

System Testing: In system testing, s/w and other system elements are tested as a whole. This
is the last high-order testing step which falls in the context of computer system engineering.
Software is combined with other system elements like H/W, People, Database and the overall
functioning is checked by conducting a series of tests. These tests fully exercise the computer
based system. The types of tests are:

1. Recovery testing: Systems must recover from faults and resume processing within a
prespecified time.
It forces the system to fail in a variety of ways and verifies that recovery is properly
performed. Here the Mean Time To Repair (MTTR) is evaluated to see if it is within
acceptable limits.
2. Security Testing: This verifies that protection mechanisms built into a system will protect it
from improper penetrations. Tester plays the role of hacker. In reality given enough resources
and time it is possible to ultimately penetrate any system. The role of system designer is to
make penetration cost more than the value of the information that will be obtained.
3. Stress testing: It executes a system in a manner that demands resources in abnormal quantity,
frequency or volume and tests the robustness of the system.
4. Performance Testing: This is designed to test the run-time performance of s/w within the
context of an integrated system. They require both h/w and s/w instrumentation.

Testing Tactics:
The goal of testing is to find errors and a good test is one that has a high probability of finding
an error.
A good test is not redundant and it should be neither too simple nor too complex.
Two major categories of software testing
Black box testing: It examines some fundamental aspect of a system, tests whether
each function of product is fully operational.
White box testing: It examines the internal operations of a system and examines
the procedural detail.

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 Black box testing
This is also called behavioural testing and focuses on the functional requirements of software. It
fully exercises all the functional requirements for a program and finds incorrect or missing
functions,interface errors, database errors etc. This is performed in the later stages in the
testing process. Treatsthe system as black box whose behaviour can be determined by studying
its input and related output Not concerned with the internal. The various testing methods
employed here are:
1) Graph based testing method: Testing begins by creating a graph of important objects and
their relationships
and then devising a series of tests that will cover the graph so that each object and relationship
is exercised and errors are uncovered.

Object

Link

Fig: O-R graph.

2) Equivalence partitioning: This divides the input domain of a program into classes of
data from which test
Cases can be derived. Define test cases that uncover classes of errors so that no. of test cases
are reduced.This is based on equivalence classes which represents a set of valid or invalid
states for inputconditions. Reduces the cost of testing

Example
Input consists of 1 to 10
Then classes are n<1,1<=n<=10,n>10
Choose one valid class with value within the allowed range and two invalid classes where
values are greater than maximum value and smaller than minimum value.

3) Boundary Value analysis

Select input from equivalence classes such that the input lies at the edge of the equivalence
classes. Set of

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 data lies on the edge or boundary of a class of input data or generates the data that lies at the
boundary of a class of output data. Test cases exercise boundary values to uncover errors at the
boundaries of the input domain.

Example
If 0.0<=x<=1.0
Then test cases are (0.0,1.0) for valid input and (-0.1 and 1.1) for invalid input

4) Orthogonal array Testing

This method is applied to problems in which input domain is relatively small but too large for
exhaustive testing
Example
Three inputs A,B,C each having three values will require 27 test cases. Orthogonal testing will
reduce the number of test case to 9 as shown below

White Box testing

Also called glass box testing. It uses the control structure to derive test cases. It exercises all
independent paths, Involves knowing the internal working of a program, Guarantees that all
independent paths will be exercised at least once .Exercises all logical decisions on their true and
false sides, Executes all loops,Exercises all data structures for their validity. White box testing
techniques
1. Basis path testing
2.Control structure
testing 1.Basis path
testing
Proposed by Tom McCabe. Defines a basic set of execution paths based on
logical complexity of a procedural design. Guarantees to execute every statement in the
program at least once Steps of Basis Path Testing
1. Draw the flow graph from flow chart of the program
2.Calculate the cyclomatic complexity of the resultant flow
graph 3.Prepare test cases that will force execution of each path
Two methods to compute Cyclomatic complexity number
1.V(G)=E-N+2 where E is number of edges, N is number of
nodes 2.V(G)=Number of regions

The structured constructs used in the flow graph are:

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 Fig: Basis path

testing Basis path testing is simple and effective

It is not sufficient in itself

2.Control Structure

testing
This broadens testing coverage and improves quality of testing. It uses the following methods:
a) Condition testing: Exercises the logical conditions contained in a program module.
Focuses on testing each condition in the program to ensure that it does not contain
errors Simple condition
E1<relation operator>E2 Compound condition
simple condition<Boolean operator>simple
condition
Types of errors include operator errors, variable errors, arithmetic expression errors etc.
b) Data flow Testing
This selects test paths according to the locations of definitions and use of variables in a
program Aims to ensure that the definitions of variables and subsequent use is tested
First construct a definition-use graph from the control flow of a program
DEF(definition):definition of a variable on the left-hand side of an assignment statement
USE: Computational use of a variable like read, write or variable on the right hand of
assignment statement Every DU chain be tested at least once.

c) Loop Testing
This focuses on the validity of loop constructs. Four categories can be defined

1.Simple
loops
2.Nested
loops

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 3.Concatenated
loops 4.Unstructured
loops

Testing of simple loops

N is the maximum number of allowable passes through the loop
1.Skip the loop entirely
2.Only one pass through the
loop 3.Two passes through the
loop
4.m passes through the loop where
m>N 5.N-1,N,N+1 passes the loop

The Art of Debugging

Debugging occurs as a consequence of successful testing. It is an action that results in the
removal of errors.
It is very much an art.

Fig: Debugging process

Debugging has two outcomes:

- cause will be found and corrected
- cause will not be
found Characteristics of
bugs:
- symptom and cause can be in different locations

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 - Symptoms may be caused by human error or timing problems

Debugging is an innate human trait. Some are good at it and some are

not.

Debugging Strategies:
The objective of debugging is to find and correct the cause of a software error which is realized
by a combination of systematic evaluation, intuition and luck. Three strategies are proposed:
1)Brute Force Method.
2)Back Tracking
3)Cause
Elimination

Brute Force: Most common and least efficient method for isolating the cause of a s/w error.
This is applied
when all else fails. Memory dumps are taken, run-time traces are invoked and program is
loaded with output statements. Tries to find the cause from the load of information Leads
to waste of time and effort.

Back tracking: Common debugging approach. Useful for small programs

Beginning at the system where the symptom has been uncovered, the source code is traced
backward until the site of the cause is found. More no. of lines implies no. of paths are
unmanageable.

Cause Elimination: Based on the concept of Binary partitioning. Data related to

error occurenec are organized to isolate potential causes. A “cause hypothesis” is
devised and data is used to prove or disprove it. A list of all possible causes is developed
and tests are conducted to eliminate each

Automated Debugging: This supplements the above approaches with debugging tools that
provide semi-automated support like debugging compilers, dynamic debugging aids, test
casegenerators, mapping tools etc.
Regression Testing: When a new module is added as part of integration testing the software
changes.
This may cause problems with the functions which worked properly before. This testing is
the re-execution of some subset of tests that are already conducted to ensure that changes
have not propagatedunintended side effects. It ensures that changes do not introduce
unintended behaviour or errors. This can be done manually or automated. Software Quality
Conformance to explicitly stated functional andperformance requirements, explicitly
documented development standards, and implicit characteristics that are expected of

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 All professionally developed software.
Factors that affect software quality can be categorized in two broad groups:
Factors that can be directly measured (e.g. defects uncovered during testing)
Factors that can be measured only indirectly (e.g. usability or maintainability)

McCall’s quality factors

1.Productoperation Correctness
Reliabilit
y
Efficienc
y
Integrity
Usability
2. Product
Revision
Maintainabilit
y Flexibility
3. Product
Transition
Portability
Reusability
Interoperability

ISO 9126 Quality Factors

1. Functionality
2.Reliability
3.Usability
4.Efficiency
5.Maintainabilit
y 6.Portability
Product metrics

Product metrics for computer software helps us to assess quality.

Measure Provides a quantitative indication of the extent, amount,
dimension, capacity or size of someattribute of a product or process
Metric(IEEE 93 definition)

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 A quantitative measure of the degree to which a system, component or process possess
a given attribute Indicator
A metric or a combination of metrics that provide insight into the software process, a
software project or a product itself
Product Metrics for analysis, Design, Test and maintenance

Product metrics for the Analysis model

Function point Metric
First proposed by Albrecht
Measures the functionality delivered by the
system FP computed from the following
parameters
1) Number of external inputs(EIS)
2) Number external outputs(EOS)

Product metrics for the Analysis model

Number of external Inquiries(EQS)
Number of Internal Logical Files(ILF)
Number of external interface
files(EIFS)
Each parameter is classified as simple, average or complex and weights are assigned as follows

Product metrics for the Analysis model

• Information
Domain Count Simple avg Complex
EIS 3 4 6
EOS 4 5 7
EQS 3 4 6
ILFS 7 10 15
EIFS 5 7 10

FP=Count total *[0.65+0.01*E(Fi)]

Metrics for Design Model

DSQI(Design Structure Quality

Index) US air force has designed the
DSQI
Compute s1 to s7 from data and architectural design

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 S1:Total number of modules
S2:Number of modules whose correct function depends on the data input
S3:Number of modules whose function depends on prior processing
S4:Number of data base items
S5:Number of unique database
items S6: Number of database
segments
S7:Number of modules with single entry and exit

Calculate D1 to D6 from s1 to s7 as follows:

D1=1 if standard design is followed otherwise
D1=0 D2(module independence)=(1-(s2/s1))
D3(module not depending on prior
processing)=(1-(s3/s1)) D4(Data base size)=(1-(s5/s4))
D5(Database compartmentalization)=(1-(s6/s4)
D6(Module entry/exit
characteristics)=(1-(s7/s1))

DSQI=sigma of WiDi

i=1 to 6,Wi is weight assigned to Di

If sigma of wi is 1 then all weights are equal to 0.167
DSQI of present design be compared with past DSQI. If DSQI is significantly lower than
the average,further design work and review are indicated

METRIC FOR SOURCE CODE

HSS(Halstead Software science)

Primitive measure that may be derived after the code is generated or estimated once design is
complete

n1 = the number of distinct operators that appear in a

program n2 = the number of distinct operands that appear in a
program N1 = the total number of operator occurrences.
N2 = the total number of operand
occurrence. Overall program length N can
be computed:
N = n1 log2 n1 + n2 log2 n2 V = N log2(n1+ n2)

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 METRIC FOR TESTING

n1 = the number of distinct operators that appear in a

program n2 = the number of distinct operands that appear in
a program N1 = the total number of operator occurrences.
N2 = the total number of operand
occurrence. Program Level and Effort
PL = 1/[(n1 / 2) x (N2 / n2 l)]
e = V/PL

METRICS FOR MAINTENANCE

Mt = the number of modules in the current release

Fc = the number of modules in the current release that have been changed
Fa = the number of modules in the current release that have been added.
Fd = the number of modules from the preceding release that were deleted in the current
release

The Software Maturity Index, SMI, is defined as:

SMI = [Mt–(Fc + Fa +Fd)/ Mt ]

Metrics for Process And Product

Software Measurement:
Software measurement can be categorized
as 1)Direct Measure and
2)Indirect Measure

Metrics for Process And

Product Direct Measurement
Direct measure of software process include cost and effort
Direct measure of product include lines of code, Execution speed, memory size, defects per
reporting time period.
Indirect Measurement
Indirect measure examines the quality of software product itself(e.g. :-Functionality,
complexity, efficiency, reliability and maintainability)

Reasons for measurement

To gain baseline for comparison with future
assessment To determine status with respect to plan
To predict the size, cost and duration estimate
To improve the product quality and process improvement

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 Software Measurement
The metrics in software Measurement
are Size oriented metrics
Function oriented
metrics Object oriented
metrics
Web based application metric

Size Oriented Metrics

It totally concerned with the measurement of software.
A software company maintains a simple record for calculating the size of the software.
It includes LOC, Effort,$$,PP document,Error,Defect ,People.
Function oriented metrics
Measures the functionality derived by the application
The most widely used function oriented metric is Function point
Function point is independent of programming language
Measures functionality from user point of view

Object oriented metric

Relevant for object oriented
programming Based on the following
Number of scenarios (Similar to use cases)
Number of key classesNumber of support
classes Number of average support class per key
class Number of subsystem

Web based application metric

Metrics related to web based application measure the following
1.Number of static pages(NSP)
2. Number of dynamic pages(NDP)
Customization(C)=NSP/NSP+NDP C should approach 1
Metrics for Software Quality
Measuring Software Quality
1.Correctness=defects/KLO
C
2.Maintainability=MTTC(Mean-time to
change) 3.Integrity=Sigma[1-(threat(1-
security))]
Threat : Probability that an attack of specific type will occur within a given time
Security : Probability that an attack of a specific type will be repelled Metrics for Software
Quality Usability: Ease of use
Defect Removal Efficiency(DRE) DRE=E/(E+D)
E is the no. of errors found before delivery and D is no. of defects reported after
delivery Ideal value of DRE is 1

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 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING

UNIT – V

Risk management: Reactive vs. Proactive Risk strategies, software risks, Risk
identification, Risk projection, Risk refinement, RMMM, RMMM Plan.
Quality Management: Quality concepts, Software quality assurance, Software Reviews,
Formal technical reviews, Statistical Software quality Assurance, The Capability
Maturity Model Integration (CMMI), Software reliability, The ISO 9000 quality
standards.

Risk Management
Risk is an undesired event or circumstance that occur while a project is underway It is
necessary for the project manager to anticipate and identify different risks that a project may be
susceptible to Risk Management. It aims at reducing the impact of all kinds of risk that may effect
a project by identifying, analyzing and managing them

Reactive Vs Proactive risk

Reactive : It monitors the projects likely risk and resources are set aside.
Proactive: Risk are identified, their probability and impact is accessed

Software Risk
It involve 2 characteristics
Uncertainty : Risk may or may not happen
Loss : If risk is reality unwanted loss or consequences will occur
It includes
1)Project Risk
2)Technical Risk
3)Business Risk
4)Known Risk
5)Unpredictable Risk
6) Predictable risk
Project risk: Threaten the project plan and affect schedule and resultant cost
Technical risk: Threaten the quality and timeliness of software to be produced
Business risk: Threaten the viability of software to be built
Known risk: These risks can be recovered from careful evaluation
Predictable risk: Risks are identified by past project experience
Unpredictable risk: Risks that occur and may be difficult to identify

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 Risk Identification
It concerned with identification of risk
Step1: Identify all possible risks
Step2: Create item check list
Step3: Categorize into risk components-Performance risk, cost risk, support risk and
schedule risk
Step4: Divide the risk into one of 4
categories Negligible-0
Marginal-1
Critical-2
Risk Identification
Risk Identification includes
Product size
Business impact
Development environment
Process definition
Customer characteristics
Technology to be built
Staff size and experience

Risk Projection
Also called risk estimation. It estimates the impact of risk on the project and the product.
Estimation is done by using Risk Table. Risk projection addresses risk in 2 ways

Prob
abili Imp RM
Risk Category ty act MM

Size
estimate PS 60% 2
may be
significantly
low

Larger no.
of PS 30% 3
users than
planned

Less reuse PS 70% 2

than planned

End user BU 40% 3

resist system

Likelihood or probability that the risk is real(Li)

Consequences(Xi)

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 Risk Projection
Steps in Risk projection
1.
Estimate Li for each risk
2.
Estimate the consequence Xi
3.
Estimate the impact
4.
Draw the risk table
Ignore the risk where the management concern is low i.e., risk having impact high or low
with low probability of occurrence
Consider all risks where management concern is high i.e., high impact with high or
moderate probability of occurrence or low impact with high probability of occurrence
Risk Projection
Projection

The impact of each risk is assessed by Impact

values Catastrophic-1 Critical-2 Marginal-3
Negligible-4

Risk Refinement
Also called Risk assessment
Refines the risk table in reviewing the risk impact based on the following three factors
a.Nature: Likely problems if risk occurs
b.Scope: Just how serious is it?
c.Timing: When and how long

It is based on Risk Elaboration

Calculate Risk exposure
RE=P*C
Where P is probability and C is cost of project if risk occurs
Risk Mitigation Monitoring And Management (RMMM)
Its goal is to assist project team in developing a strategy for dealing with
risk There are three issues of RMMM
1) Risk Avoidance
2)Risk Monitoring
and 3)Risk
Management

Risk Mitigation Monitoring And Management (RMMM)

Risk Mitigation
Proactive planning for risk
avoidance Risk Monitoring
Assessing whether predicted risk occur or not
Ensuring risk aversion steps are being properly
applied Collection of information for future risk
analysis Determine which risks caused which
problems
Risk Mitigation Monitoring And Management (RMMM)
Risk ManagementContingency planning
Actions to be taken in the event that mitigation steps have failed and the risk has
become a live problem Devise RMMP(Risk Mitigation Monitoring And Management Plan)

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 RMMM plan
It documents all work performed as a part of risk analysis.
Each risk is documented individually by using a Risk Information Sheet.
RIS is maintained by using a database system Quality Management

Quality Concepts
Variation control is the heart of quality control
Form one project to another, we want to minimize the difference between the predicted
resources needed to complete a project and the actual resources used, including staff,
equipment, and calendar time
Quality of design
Refers to characteristics that designers specify for the end
product Quality Management
Quality of conformance
Degree to which design specifications are followed in manufacturing the product
Quality control
Series of inspections, reviews, and tests used to ensure conformance of a work product to its
specifications
Quality assurance
Consists of a set of auditing and reporting functions that assess the effectiveness and
completeness of quality control activities

Cost of Quality
Prevention costs
Quality planning, formal technical reviews, test equipment, training
Appraisal costs
In-process and inter-process inspection, equipment calibration and maintenance, testing
Failure costs
rework, repair, failure mode
analysis External failure costs
Complaint resolution, product return and replacement, help line support, warranty work
Software Quality Assurance
Software quality assurance (SQA) is the concern of every software engineer to reduce
cost and improve product time-to-market.
A Software Quality Assurance Plan is not merely another name for a test plan, though
test plans are
included in an SQA plan.
SQA activities are performed on every software project.
Use of metrics is an important part of developing a strategy to improve the quality of
both software processes and work products.

Software Quality Assurance

Definition of Software Quality serves to emphasize:
Conformance to software requirements is the foundation from which software quality is
measured.

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 Specified standards are used to define the development criteria that are used to guide the
manner in which software is engineered.
Software must conform to implicit requirements (ease of use, maintainability, reliability,
etc.) as well as its explicit requirements.

SQA Activities
Prepare SQA plan for the project.
Participate in the development of the project's software process description.
Review software engineering activities to verify compliance with the defined software
process.
Audit designated software work products to verify compliance with those defined as part
of the software process.

Ensure that any deviations in software or work products are documented and handled
according to a documented procedure.
Record any evidence of noncompliance and reports them to management.

Software Reviews
Purpose is to find errors before they are passed on to another software engineering
activity or released to the customer.
Software engineers (and others) conduct formal technical reviews (FTRs) for software
quality assurance.
Using formal technical reviews (walkthroughs or inspections) is an effective means for
improving software quality.

Formal Technical Review

A FTR is a software quality control activity performed by software engineers and
others.The objectives are:
To uncover errors in function, logic or implementation for any representation of the
software.
To verify that the software under review meets its requirements.
To ensure that the software has been represented according to predefined standards.
To achieve software that is developed in a uniform manner and
To make projects more manageable.

Review meeting in FTR

The Review meeting in a FTR should abide to the following constraints
Review meeting members should be between three and five.
Every person should prepare for the meeting and should not require more than two hours of
work for each person.
The duration of the review meeting should be less than two hours.
The focus of FTR is on a work product that is requirement specification, a detailed
component design, a source code listing for a component.
The individual who has developed the work product i.e, the producer informs the project
leader that the work product is complete and that a review is required.
The project leader contacts a review leader, who evaluates the product for readiness,
generates copy of product material and distributes them to two or three review members for
advance preparation .

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 Each reviewer is expected to spend between one and two hours reviewing the product,
making notes
The review leader also reviews the product and establish an agenda for the review meeting
The review meeting is attended by review leader, all reviewers and the producer.
One of the reviewer act as a recorder,who notes down all important points discussed in
the meeting.
The meeting(FTR) is started by introducing the agenda of meeting and then the
producer introduces his product. Then the producer “walkthrough” the product, the
reviewers raise issues which they have prepared in advance.
If errors are found the recorder notes down

Review reporting and Record keeping

During the FTR, a reviewer( recorder) records all issues that have been raised
A review summary report answers three questions
What was reviewed?
Who reviewed it?
What were the findings and conclusions?
Review summary report is a single page form with possible attachments

The review issues list serves two purposes

To identify problem areas in the product
To serve as an action item checklist that guides the producer as corrections are made

Review Guidelines
Review the product, not the producer
Set an agenda and maintain it
Limit debate and rebuttal
Enunciate problem areas, but don’t attempt to solve every problem noted
Take return notes
Limit the number of participants and insist upon advance preparation.
Develop a checklist for each product i.e likely to be reviewed
Allocate resources and schedule time for FTRS
Conduct meaningful training for all reviewer
Review your early reviews
Software Defects
Industry studies suggest that design activities
introduce 50-65% of all defects or errors
during the software process
Review techniques have been shown to be up
to 75% effective in uncovering design flaws
which ultimately reduces the cost of
subsequent activities in the software process

Statistical Quality Assurance

Information about software defects is collected and categorized.
Each defect is traced back to its cause
Using the Pareto principle (80% of the defects can be traced to 20% of the causes)
isolate the "vital few" defect causes.

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 Move to correct the problems that caused the defects in the "vital few”

Six Sigma for Software Engineering

The most widely used strategy for statistical quality
assurance Three core steps:
1. Define customer requirements, deliverables, and project goals via well-
defined methods of customer communication.
2. Measure each existing process and its output to determine current
quality performance (e.g., compute defect metrics)
3. Analyze defect metrics and determine vital few causes.

For an existing process that needs improvement

1. Improve process by eliminating the root causes for defects
2. Control future work to ensure that future work does not reintroduce causes of
defects
If new processes are being developed
1. Design each new process to avoid root causes of defects and to
meet customer requirements
2. Verify that the process model will avoid defects and meet customer
requirements
Software Reliability
Defined as the probability of failure free operation of a
computer program in a specified environment for a specified
time period
Can be measured directly and estimated using historical and
developmental data
Software reliability problems can usually be traced back to
errors in design or implementation.
Measures of Reliability
Mean time between failure (MTBF) = MTTF + MTTR
MTTF = mean time to failure
MTTR = mean time to repair
Availability = [MTTF / (MTTF + MTTR)] x 100%

ISO 9000 Quality Standards

ISO (International Standards Organization) is a group or consortium of 63 countries
established to plan and fosters standardization. ISO declared its 9000 series of standards in
1987. It serves as a reference for the contract between independent parties. The ISO 9000
standard determines the guidelines for maintaining a quality system. The ISO standard
mainly addresses operational methods and organizational methods such as responsibilities,
reporting, etc. ISO 9000 defines a set of guidelines for the production process and is not
directly concerned about the product itself.

Types of ISO 9000 Quality Standards

The ISO 9000 series of standards is based on the assumption that if a proper stage is
followed for production, then good quality products are bound to follow automatically. The
types of industries to which the various ISO standards apply are as follows.

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 1. ISO 9001: This standard applies to the organizations engaged in design,
development, production, and servicing of goods. This is the standard that applies to
most software development organizations.
2. ISO 9002: This standard applies to those organizations which do not design products but
are only involved in the production. Examples of these category industries contain steel
and car manufacturing industries that buy the product and plants designs from external
sources and are engaged in only manufacturing those products. Therefore, ISO 9002 does
not apply to software development organizations.
3. ISO 9003: This standard applies to organizations that are involved only in the
installation and testing of the products. For example, Gas companies.

An organization determines to obtain ISO 9000 certification applies to ISO registrar office for
registration. The process consists of the following stages:

1.Application: Once an organization decided to go for ISO certification, it applies to the registrar
for registration.

2.Pre-Assessment: During this stage, the registrar makes a rough assessment of the organization.

3.Document review and Adequacy of Audit: During this stage, the registrar reviews the
document submitted by the organization and suggest an improvement.

4.Compliance Audit: During this stage, the registrar checks whether the organization has compiled the
suggestion made by it during the review or not.

5.Registration: The Registrar awards the ISO certification after the successful completion of all
the phases.

6. Continued Inspection: The registrar continued to monitor the organization time by time.

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