Software Engineering

Lecture 2: Software Development Life Cycle

© Fall 2024 – Dr. Alyaa Hamza

Alyaa.hamza@sut.edu.eg
What is an information system (IS)?

Hardware, software, data, System—Set of components

people, and procedures that that interact to achieve
work together to produce common goal
quality information
Businesses use many types of
systems
What are the phases of the system development
cycle?

Phase 2. Analysis
▪ Conduct preliminary investigation
Phase 1. Planning ▪ Perform detailed analysis activities:
Phase 3. Design
▪ Review project requests Study current system ▪ Acquire
▪ Prioritize project Determine user requirements hardware and
requests software, if
Recommend solution
▪ Allocate resources necessary
▪ Identify project ▪ Develop details
development team of system

Phase 5. Support Phase 4. Implementation

▪ Conduct post-implementation ▪ Develop programs, if necessary
system review ▪ Install and test new system
▪ Identify errors and enhancements ▪ Train users
▪ Monitor system performance ▪ Convert to new system
What are guidelines for system development?

Arrange tasks into phases

(groups of activities)
Involve users (anyone for whom
system is being built)

Develop clearly defined standards (procedures

company expects employees to follow)
Who participates in the system development life
cycle?
What is a systems analyst?

Responsible for designing and

developing information system

Communicate between users and

IT professionals
What is the project team?

Formed to work on project from beginning to end

Consists of users, systems analyst, and other IT professionals

Project leader—one member of the team who

manages and controls project budget and schedule
What is feasibility?
Operational
feasibility
Measure of
how suitable
system Four feasibility
development tests:
will be to the Schedule
company feasibility

Economic
feasibility
(also called Technical
cost/benefit feasibility
feasibility)
What is documentation?

Collection and summarization

of data and information

Includes reports, diagrams,

programs, and other deliverables
What are six data and information gathering
techniques?

➢ Review documentation
➢ Observe
➢ Questionnaire
➢ Interview
➢ Joint-application
design (JAD) session
➢ Research
What are some reasons to create or modify an information system?

To correct problem To improve

in existing system existing system

Outside group may Competition can

mandate change lead to change
What is a request for system services?

➢ Formal request for

new or modified
information system
▪ Also called
project request
What is the planning phase?

Begins when steering committee receives project request

Steering committee—
decision-making body
for the company

Function of committee:

Form project
Review and development
Prioritize Allocate
approve project team for each
project requests resources
requests approved
project
What is the analysis phase?

Conduct preliminary Perform detailed

investigation, also analysis
called feasibility
study
What is the preliminary investigation?

➢ Determine exact nature of problem or improvement and whether it

is worth pursuing

▪ Findings are presented in feasibility report, also known as a feasibility study

What is detailed analysis?

1. Study how current system

works

2. Determine user’s wants, needs,

and requirements

3. Recommend solution

Sometimes called logical design

What is the Assesses
feasibility
of each

system alternative
solution

proposal? Recommends
the most
Presented to
steering
committee,
feasible which decides
solution for how system will
the project be developed
What are possible solutions?

Horizontal market
software—meets needs of
many companies
Buy packaged software—prewritten
software available for purchase
Vertical market
software—designed for
particular industry
Write own custom software—software
developed at user’s request

Outsource—have outside source

develop software
What is the design phase?

Acquire hardware and software

Develop all details of new or

modified information system
What is needed to acquire new hardware and software?
➢ Identify all hardware and software requirements of new or
modified system

Talk with other

Search Web
systems analysts

Read print and online

Visit vendors’ stores trade journals,
newspapers, and
magazines
What is a detailed design?

Detailed design specifications for components in proposed solution

Includes several activities

Database Input and Program

design output design design
What is a mockup?

➢ Sample of input or output that contains actual data

What is a prototype?

Working model of
proposed system

Beginning a prototype too early

may lead to problems
What is computer-aided software engineering (CASE)?

➢ Software tools designed to support activities of system

development cycle
What is the implementation phase?

➢ Purpose is to construct, or build, new or modified

system and then deliver it to users
Convert to new system

Train users

Install and test new system

Develop programs
What are the three types of tests performed by system developers?

Unit Test Systems test

Verifies each Verifies all programs

individual program in application work
works by itself together

Integration Test

Verifies application
works with other
applications
What is training?

➢ Showing users exactly

how they will use new
hardware and software
in system
What is the support phase?

➢ Provides ongoing assistance after system is implemented

Conduct post-implementation system review—meeting to find out if
information system is performing according to expectations

Identify errors

Identify enhancements

Monitor system performance

The Software Development Life Cycle
Software-
Development Life- Reuse-Oriented Spiral Model
Cycle Models Development
Processes

V Process Model
Waterfall Model Iterative Delivery Model

Iterative
Prototyping Model Enhancement
Model
 1- Waterfall Process Model

➢The waterfall model is a very common software

development process model.
➢Because of the cascade from one phase to another, this
model is known as the waterfall model.
➢Each phase, in turn, is structured as a set of activities
that might be executed by different people concurrently.
➢The waterfall model is illustrated in the next Figure
Waterfall Process Model
 Waterfall Process Model

1. Feasibility Study:
➢ The purpose of this phase is to produce a feasibility study
document that evaluates the costs and benefits of the
proposed application.
➢ The feasibility study is usually done within limited time
bounds and under pressure.
➢ Often, its result is an offer to the potential customer.
➢ At the end of this phase, a report called a feasibility study is
prepared by a group of software engineers.
➢ This report determines whether the project is feasible or not.
 Waterfall Process Model
2. Requirement Analysis and Specification:
➢ This phase exactly tells the requirements and needs of the
project.
➢ The purpose of a requirements analysis is to identify the
qualities required of the application, in terms of functionality,
performance, ease of use, portability, and so on.
➢ The requirements describe the “what” of a system, not the
“how.”
➢ The resultant document is known as the software requirement
specification (SRS) document.
 Waterfall Process Model

3. Design and Specification:

➢ The goal is to transform the requirements specified in the SRS
document into a structure that is suitable for implementation in
some programming language.

4. Coding and Module Testing:

➢ Is the phase in which we actually write programs using a
programming language.
➢ The output of this phase is an implemented and tested collection of
modules.
 Waterfall Process Model

5. Integration and System Testing:

➢ The modules are integrated in a planned manner.
➢ The different modules making up a software product.
➢ Integration is normally carried out incrementally over a number of
steps.
➢ During each integration step, the partially integrated system is
tested and a set of previously planned modules are added to it.
➢ Finally, when all the modules have been successfully integrated
and tested, system testing is carried out.
 Waterfall Process Model

➢ The objective of system testing is to determine whether the

software system performs per the requirements mentioned in
the SRS document.
➢ This testing is known as system testing.
➢ A fully developed software product is system tested. The system
testing is done in three phases: Alpha, Beta, and Acceptance
Testing.
➢ Alpha Testing is conducted by the software-development team
at the developer’s site.
 Waterfall Process Model
➢ Beta Testing is performed by a group of friendly customers in the
presence of the software-development team.

➢ Acceptance Testing is performed by the customers themselves. If

the software is successful in acceptance testing, the product is
installed at the customer’s site.
Waterfall Process Model

6. Delivery and Maintenance:

➢ The delivery of software is often done in two stages.
▪ In the first stage, the application is distributed
among a selected group of customers prior to its
official release.
o The purpose of this procedure is to perform a
kind of controlled experiment to determine, on
the basis of feedback from users, whether any
changes are necessary prior to the official
release.
▪ In the second stage, the product is distributed to the
customers.
 Waterfall Process Model
Advantages of Waterfall Model
➢ The main advantage is its simplicity
➢ It is straightforward and divides the large task of building a software
system into a series of cleanly divided phases, each phase dealing
with a separate logical concern
➢ Waterfall model is also easy to administer in a contractual setup.
➢ As each phase is completed and its work product produced, some
amount of money is given by the customer to the developing
organization
Waterfall Process Model
Disadvantages of Waterfall Model
➢ It assumes that the requirements of a system can be
frozen before the design begins (having unchanging
requirements is unrealistic for some projects)
➢ Freezing the requirements usually requires choosing the
hardware (due to the speed at which hardware
technology is changing, it is likely that the final software
will use a hardware technology on the verge of becoming
obsolete).
➢ This is clearly not desirable for such expensive software
systems.
Waterfall Process Model

● It follows the “big bang” approach. The entire software is delivered in one shot
at the end.
● If the project runs out of money in the middle, then there will be no software.
That is, it has the “all or nothing” value proposition.
● It encourages “requirements bloating”
● Since all requirements must be specified at the start, it encourages the users
and other stakeholders to add even those features which they think might be
needed.
 Waterfall Process Model

➢ Despite these limitations, the waterfall model has been the

most widely used process model
➢ If the developing organization is quite familiar with the problem
domain and the requirements for the software are quite clear,
the waterfall model works well, and may be the most efficient
process
When to use the Waterfall Model
• Requirements are very well known
• Product definition is stable
• Technology is understood
• New version of an existing product
• Porting an existing product to a new platform.
2- Prototyping Process Model

➢ The goal of a prototyping-based development process is to counter the first

limitation of the waterfall model
➢ The basic idea here is that instead of freezing the requirements before any
design or coding can proceed, a throwaway prototype is built to help
understand the requirements
➢ Prototyping is an attractive idea for complicated and large systems.
➢ This might be needed for novel systems, where it is not clear that constraints
can be met or that algorithms can be developed to implement the
requirements
 Prototyping
Process Model

➢ The Prototyping model

is illustrated in the
Figure below
Prototyping Process Model

➢ After the prototype has been developed, the users are given an opportunity to use and explore the
prototype

➢ They provide feedback to the developers regarding the prototype: What is correct, what needs to be
modified, what is missing, what is not needed, etc.

➢ Based on the feedback, the prototype is modified to incorporate some of the suggested changes that
can be done easily, and then the users and the clients are again allowed to use the system

➢ This cycle repeats until we reach the requirements needed

Advantages of
Prototyping Model

➢ Suitable for large systems for which

there is no manual process to define
the requirements
➢ User training to use the system
➢ Quality of software is good
➢ Requirements are not freezed
3- Iterative Model
➢ The iterative development process model
tries to combine the benefits of both
prototyping and the waterfall model.

➢ Two common approaches for iterative

development model:

A. Iterative-
Enhancement model
B. Iterative Delivery
model
 A. Iterative Enhancement Model

➢ The iterative-enhancement model combines elements of the linear sequential model (Waterfall) with the
iterative philosophy of prototyping

➢ The software is broken down into several modules, which are incrementally developed and delivered

1. The development team develops the core module of the system

2. It is later refined into increasing levels of capability of adding new functionalities in successive versions
Iterative Enhancement Model

➢ Each linear sequence produces a deliverable increment of the software

➢ For example, word-processing software developed using the iterative paradigm might
deliver basis file management, editing, and document production functions in the first
increment. More sophisticated editing and document production capabilities in the
second increment; and spelling and grammar checking in the third increment
Advantages of Iterative Enhancement Model

➢ The feedback from early increments improve the later stages

➢ The possibility of changes in requirements is reduced
➢ Users get benefits earlier than with a conventional approach
➢ Early delivery of some useful components improves cash flow
➢ Smaller sub-projects are easier to control and manage
➢ The project can be temporarily abandoned if more urgent work crops up
➢ Job satisfaction is increased for developers
Disadvantages of Iterative Enhancement Model

➢ Later increments may require modifications to earlier increments

➢ Programmers may be more productive working on one large system
than on a series of smaller ones
➢ Some problems are difficult to divide into functional units (modules)
B. Iterative Delivery Model

➢ In this approach, the requirements and the architecture design is done in a standard waterfall or
prototyping approach, but deliver the software iteratively
➢ That is, the building of the system, is done iteratively, though most of the requirements are
specified upfront
➢ We can view this approach as having one iteration delivering the requirements and the
architecture plan, and then further iterations delivering the software in increments.
Iterative Delivery Model

➢ At the start of each delivery iteration, requirements which will be

implemented in this release are decided, and then the design is
enhanced and code developed to implement the requirements
➢ The iteration ends with delivery of a working software system providing
some value to the end user
Iterative
Delivery
Model
.
4- Component-Based (Reuse-Oriented) Development

➢ In the majority of software projects, there is some software reuse

➢ This usually happens when people working on the project know of designs or code
which is similar to that required
➢ They look for these, modify them as required and incorporate them into their
system
➢ This reuse-oriented approach relies on a large base of reusable software
components.
Reuse-Oriented Development Processes
➢ Sometimes, these components are systems in their own right that may provide specific functionality
such as text formatting or numeric calculation.

➢ The generic process model for component-based software engineering (CBSE) is shown in the next
Figure
Reuse-Oriented Development Processes
➢While the initial requirements specification
stage and the validation stage are comparable
with other processes, the intermediate stages in
a reuse-oriented process are different.

➢These stages are as follows:

 Reuse-Oriented Development Processes
1.Component analysis: Given the requirements specification,
a search is made for components to implement that
specification.
2.Requirements modification: During this stage, the
requirements are analyzed using information about the
components that have been discovered. They are then
modified to reflect the available components.
3.System design with reuse: During this phase, the
framework of the system is designed or an existing
framework is reused.
4.Development and integration: Software that cannot be
externally procured is developed, and the components and
COTS systems are integrated to create the new system.
 5- Spiral Model
➢Rather than represent the software process as a sequence of
activities with some backtracking from one activity to another,
the process is represented as a spiral.
➢Each loop in the spiral represents a phase of the software
process.
➢Thus, the innermost loop might be concerned with system
feasibility, the next loop with requirements definition, the next
loop with system design and so on.
Spiral Model
Spiral Model
 Spiral Model

➢Each loop in the spiral is split into four sectors:

1. Objective setting: Specific objectives for that phase of the project are defined.
Constraints on the process and the product are identified and a detailed
management plan is drawn up. Project risks are identified. Alternative
strategies, depending on these risks, may be planned.

2. Risk assessment and reduction: For each of the identified project risks, a
detailed analysis is carried out. Steps are taken to reduce the risk. For
example, if there is a risk that the requirements are inappropriate, a prototype
system may be developed.
 Spiral Model

3. Development and validation: After risk evaluation, a development

model for the system is chosen. For example, if user interface risks are
dominant, an appropriate development model might be evolutionary
prototyping. If safety risks are the main consideration, development
based on formal transformations may be the most appropriate and so
on.
4. Planning: The project is reviewed and a decision made whether to
continue with a further loop of the spiral. If it is decided to continue,
plans are drawn up for the next phase of the project.
 Advantages of Spiral Model

➢It is risk-driven model.

➢It is very flexible.
➢Less documentation is needed.
➢It uses prototyping.
Disadvantages of Spiral Model
➢No strict standards for software development.
➢No particular beginning or end of a particular
phase.
6- V Process Model
 V Process Model
➢The V model is a variant of the waterfall model
➢It represents a tacit recognition that there are
testing activities occurring throughout the waterfall
software life cycle model and not just during the
software testing period
➢For example, during requirements specification, the
requirements are evaluated for testability and an
STRS may be written
➢This document would describe the strategy
necessary for testing the requirements
 V Process Model
➢Testing is a full life-cycle activity and that it is
important to constantly consider the testability of
any software requirement and to design to allow
for such testability
Quality – the degree to which the software satisfies
stated and implied requirements

• Absence of system crashes

• Correspondence between the software and the users’
expectations
• Performance to specified requirements

Quality must be controlled because it lowers production speed,

increases maintenance costs and can adversely affect
business
Quality Assurance Plan
• Defect tracing – keeps track of each defect found, its source, when it was
detected, when it was resolved, how it was resolved, etc
• Unit testing – each individual module is tested
• Source code tracing – step through source code line by line
• Technical reviews – completed work is reviewed by peers
• Integration testing -- exercise new code in combination with code that
already has been integrated
• System testing – execution of the software for the purpose of finding
defects.