Chapter 2 software development life cycle models

Software Engineering (3rd ed.), By K.K Aggarwal & Yogesh Singh, Copyright © New Age International Publishers, 2007

1

Software Life Cycle Models

The goal of Software Engineering is to provide
models and processes that lead to the
production of well-documented maintainable
software in a manner that is predictable.


2

Software Life Cycle Models

“The period of time that starts when a software product is conceived
and ends when the product is no longer available for use. The
software life cycle typically includes a requirement phase, design
phase, implementation phase, test phase, installation and check out
phase, operation and maintenance phase, and sometimes retirement
phase”.


3

Build & Fix Model
Product is constructed without
specifications or any attempt at
design
Adhoc approach and not well
defined

Build
Code

Simple two phase model


Fix

4

Build & Fix Model

Suitable for small programming exercises of 100 or 200 lines
Unsatisfactory for software for any reasonable size
Code soon becomes unfixable & unenhanceable
No room for structured design
Maintenance is practically not possible


5

Waterfall Model
Requirement
Analysis & Specification

Design

This model is named “waterfall
model” because its diagrammatic
representation resembles a cascade of
waterfalls.
Implementation
and unit testing
Integr ation and
system testing
Operation and
maintenance


6

Waterfall Model

This model is easy to understand and reinforces
the notion of “define before design” and “design
before code”.
The model expects complete & accurate
requirements early in the process, which is
unrealistic


7

Waterfall Model
Problems of waterfall model
i.

It is difficult to define all requirements at the beginning of a
project

ii. This model is not suitable for accommodating any change
iii. A working version of the system is not seen until late in
the project’s life
iv. It does not scale up well to large projects.
v. Real projects are rarely sequential.

8

Incremental Process Models
They are effective in the situations where requirements are
defined precisely and there is no confusion about the
functionality of the final product.
After every cycle a useable product is given to the customer.
Popular particularly when we have to quickly deliver a limited
functionality system.


9

Iterative Enhancement Model
This model has the same phases as the waterfall model, but with
fewer restrictions. Generally the phases occur in the same order as
in the waterfall model, but they may be conducted in several cycles.
Useable product is released at the end of the each cycle, with each
release providing additional functionality.
Customers and developers specify as many requirements as
possible and prepare a SRS document.
Developers and customers then prioritize these requirements
Developers implement the specified requirements in one or
more cycles of design, implementation and test based on the
defined priorities.

10

Iterative Enhancement Model
Requirements
specification

Architectural
design

Detailed

design

Implementation
and unit testing

Integration
and testing

Operation and
Maintenance


11

The Rapid Application Development (RAD) Model
o
o

Developed by IBM in 1980
User participation is essential

The requirements
specification was
defined like this

The developers
understood it in
that way

This is how the
problem was
solved before.

This is how the
problem is
solved now

This is how the program is This, in fact, is what the
described by marketing
customer wanted …
That is the program after
debugging Engineering (3 ed.), By K.K Aggarwaldepartment © New Age International Publishers, 2007
Software
& Yogesh Singh, Copyright
rd

12

o

Build a rapid prototype

o

Give it to user for evaluation & obtain feedback

o

Prototype is refined
With active participation of users

Requirements
Planning

User
Description

Construction


Cut over

13


Not an appropriate model in the absence of user
participation.
Reusable components are required to reduce development
time.
Highly specialized & skilled developers are required and
such developers are not easily available.


14

Evolutionary Process Models
Evolutionary process model resembles iterative enhancement
model. The same phases as defined for the waterfall model occur
here in a cyclical fashion. This model differs from iterative
enhancement model in the sense that this does not require a
useable product at the end of each cycle. In evolutionary
development, requirements are implemented by category rather
than by priority.
This model is useful for projects using new technology that is not
well understood. This is also used for complex projects where all
functionality must be delivered at one time, but the requirements
are unstable or not well understood at the beginning.


15

Evolutionary Process Model
Concurr ent
activities

Specification

Outline
description

Initial
version

Development

Intermediate
versions

Validation

Final
version


16

Prototyping Model

The prototype may be a usable program but is not suitable as
the final software product.
The code for the prototype is thrown away. However
experience gathered helps in developing the actual system.
The development of a prototype might involve extra cost, but
overall cost might turnout to be lower than that of an
equivalent system developed using the waterfall model.


17

Prototyping Model

• Linear model
• “Rapid”


18

Spiral Model
Models do not deal with uncertainly which is inherent to software
projects.
Important software projects have failed because project risks were
neglected & nobody was prepared when something unforeseen
happened.
Barry Boehm recognized this and tired to incorporate the “project
risk” factor into a life cycle model.
The result is the spiral model, which was presented in 1986.


19

Spiral Model


20

Spiral Model
The radial dimension of the model represents the cumulative costs.
Each path around the spiral is indicative of increased costs. The
angular dimension represents the progress made in completing each
cycle. Each loop of the spiral from X-axis clockwise through 360o
represents one phase. One phase is split roughly into four sectors of
major activities.
Planning: Determination
constraints.

of

objectives,

alternatives

&

Risk Analysis: Analyze alternatives and attempts to identify
and resolve the risks involved.
Development: Product development and testing product.
Assessment: Customer evaluation

21

Spiral Model
An important feature of the spiral model is that each phase is
completed with a review by the people concerned with the
project (designers and programmers)
The advantage of this model is the wide range of options to
accommodate the good features of other life cycle models.
It becomes equivalent to another life cycle model in
appropriate situations.
The spiral model has some difficulties that need to be resolved
before it can be a universally applied life cycle model. These
difficulties include lack of explicit process guidance in determining
objectives, constraints, alternatives; relying on risk assessment
expertise; and provides more flexibility than required for many
applications.

22

The Unified Process
• Developed by I.Jacobson, G.Booch and J.Rumbaugh.
• Software engineering process with the goal of producing good
quality maintainable software within specified time and budget.

• Developed through a series of fixed length mini projects called
iterations.
• Maintained and enhanced by Rational Software Corporation and
thus referred to as Rational Unified Process (RUP).


23

Phases of the Unified Process

Inception

Elaboration

Construction

Transition

Time

Definition of
objectives
of the project

Planning &
architecture
for the project

Initial
operational
capability


Release of
the Software
product

24

Phases of the Unified Process
• Inception: defines scope of the project.
• Elaboration
- How do we plan & design the project?
- What resources are required?
- What type of architecture may be suitable?
• Construction: the objectives are translated in design &
architecture documents.
• Transition : involves many activities like delivering, training,
supporting, and maintaining the product.


25

Initial development & Evolution Cycles

V1

Inception

Elaboration

Construction

Transition

Initial development Cycle

Inception

Elaboration

Construction

Transition

V2

Evolution Cycle

Inception

Elaboration

Construction

Transition

V3

Continue till the product is retired

V1=version1, V2 =version2, V3=version3

26

Iterations & Workflow of Unified Process


27

Inception Phase
The inception phase has the following objectives:
Gathering and analyzing the requirements.
Planning and preparing a business case and evaluating
alternatives for risk management, scheduling resources etc.
Estimating the overall cost and schedule for the project.
Studying the feasibility and calculating profitability of the
project.


28

Outcomes of Inception Phase

Project plan

Prototypes
Business
model
Vision
document

Inception

Initial risk
assessment

Initial business
case
Initial
Initial use
case model project
Glossary


29

Elaboration Phase
The elaboration phase has the following objectives:
Establishing architectural foundations.
Design of use case model.
Elaborating the process, infrastructure & development
environment.
Selecting component.
Demonstrating that architecture support the vision at
reasonable cost & within specified time.


30

Outcomes of Elaboration Phase

Development plan
Preliminary
User manual
Use case
model

Elaboration

Supplementary
Requirements
with non functional
requirement

Revised risk
document
An executable
architectural
prototype
Architecture
Description
document


31

Construction Phase
The construction phase has the following objectives:
Implementing the project.
Minimizing development cost.
Management and optimizing resources.
Testing the product
Assessing the product releases against acceptance criteria


32

Outcomes of Construction Phase
Test
Outline
Documentation
manuals
Software
product

Operational
manuals
Construction

User manuals

Test Suite
A description
of the
current release


33

Transition Phase
The transition phase has the following objectives:
Starting of beta testing
Analysis of user’s views.
Training of users.
Tuning activities including bug fixing and enhancements for
performance & usability
Assessing the customer satisfaction.


34

Outcomes of Transition Phase

Transition

Product
release

Beta test reports

User feedback


35

Selection of a Life Cycle Model
Selection of a model is based on:
a) Requirements
b) Development team
c) Users
d) Project type and associated risk


36

Based On Characteristics Of Requirements
Requirements

Waterfall

Prototype

Are requirements
easily understandable
and defined?

Yes

No

No

Do we change
requirements quite
often?

No

Yes

Can we define
requirements early
in the cycle?

Yes

No

Requirements are
indicating a complex
system to be built

No

Yes

Iterative
enhancement

Evolutionary
development

Spiral

RAD

No

No

Yes

No

No

Yes

No

Yes

Yes

No

Yes

Yes

Yes

Yes

No


37

Based On Status Of Development Team
Development
team

Waterfall

Prototype

Iterative
enhancement

Evolutionary
development

Spiral

RAD

Less experience on
similar projects?

No

Yes

No

No

Yes

No

Less domain
knowledge (new to
the technology)

Yes

No

Yes

Yes

Yes

No

Less experience on
tools to be used

Yes

No

No

No

Yes

No

Availability of
training if required

No

No

Yes

Yes

No

Yes


38

User’
Based On User’s Participation
Involvement
of Users

Waterfall

Prototype

Iterative
enhancement

Evolutionary
development

Spiral

RAD

User involvement
in all phases

No

Yes

No

No

No

Yes

Limited user
participation

Yes

No

Yes

Yes

Yes

No

No

Yes

Yes

Yes

Yes

No

No

Yes

Yes

Yes

No

Yes

User have no
previous experience
of participation in
similar projects
Users are experts
of problem domain


39

Based On Type Of Project With Associated Risk
Project type
and risk

Waterfall

Prototype

Iterative
enhancement

Evolutionary
development

Spiral

RAD

Project is the
enhancement of the
existing system

No

No

Yes

Yes

No

Yes

Funding is stable
for the project

Yes

Yes

No

No

No

Yes

High reliability
requirements

No

No

Yes

Yes

Yes

No

No

Yes

Yes

Yes

Yes

Yes

No

Yes

No

No

Yes

Yes

No

Yes

No

No

Yes

No

Tight project
schedule
Use of reusable
components
Are resources
(time, money,
people etc.) scare?


40

Multiple Choice Questions
Note: Select most appropriate answer of the following questions:
2.1 Spiral Model was developed by
(a) Bev Littlewood
(b) Berry Boehm
(c) Roger Pressman
(d) Victor Basili
2.2 Which model is most popular for student’s small projects?
(a) Waterfall model
(b) Spiral model
(c) Quick and fix model
(d) Prototyping model
2.3 Which is not a software life cycle model?
(a) Waterfall model
(b) Spiral model
(c) Prototyping model
(d) Capability maturity model
2.4 Project risk factor is considered in
(a) Waterfall model
(b) Prototyping model
(c) Spiral model
(d) Iterative enhancement model
2.5 SDLC stands for
(a) Software design life cycle
(b) Software development life cycle
(c) System development life cycle
(d) System design life cycle


41

2.6 Build and fix model has
(a) 3 phases
(c) 2 phases
2.7 SRS stands for
(a) Software requirements specification
(c) System requirements specification
2.8 Waterfall model is not suitable for
(a) small projects
(c) complex projects
2.9 RAD stands for
(a) Rapid application development
(c) Ready application development
2.10 RAD model was proposed by
(a) Lucent Technologies
(c) IBM

(b) 1 phase
(d) 4 phases
(b) Software requirements solution
(d) none of the above
(b) accommodating change
(d) none of the above
(b) Relative application development
(d) Repeated application development
(b) Motorola
(d) Microsoft


42

2.11 If requirements are easily understandable and defined,which model is best suited?
(a) Waterfall model
(c) Spiral model
(d) None of the above
2.12 If requirements are frequently changing, which model is to be selected?
(a) Waterfall model
(c) RAD model
(d) Iterative enhancement model
2.13 If user participation is available, which model is to be chosen?
(a) Waterfall model
(b) Iterative enhancement model
(c) Spiral model
(d) RAD model
2.14 If limited user participation is available, which model is to be selected?
(a) Waterfall model
(b) Spiral model
(c) Iterative enhancement model
(d) any of the above
2.15 If project is the enhancement of existing system, which model is best suited?
(a) Waterfall model
(d) Spiral model


43

2.16 Which one is the most important feature of spiral model?
(a) Quality management
(b) Risk management
(c) Performance management
(d) Efficiency management
2.17 Most suitable model for new technology that is not well understood is:
(a) Waterfall model
(b) RAD model
(d) Evolutionary development model
2.18 Statistically, the maximum percentage of errors belong to the following phase of
SDLC
(a) Coding
(b) Design
(c) Specifications
(d) Installation and maintenance
2.19 Which phase is not available in software life cycle?
(a) Coding
(b) Testing
(c) Maintenance
(d) Abstraction
2.20 The development is supposed to proceed linearly through the phase in
(a) Spiral model
(b) Waterfall model
(c) Prototyping model


44

2.21 Unified process is maintained by
(a) Infosys
(b) Rational software corporation
(c) SUN Microsystems
2.22 Unified process is
(a) Iterative
(b) Incremental
(c) Evolutionary
(d) All of the above
2.23 Who is not in the team of Unified process development?
(a) I.Jacobson
(b) G.Booch
(c) B.Boehm
(d) J.Rumbaugh
2.24 How many phases are in the unified process?
(a) 4
(b) 5
(c) 2
2.25 The outcome of construction phased can be treated as:
(a) Product release
(b) Beta release
(c) Alpha release
(d) All of the above


45

Exercises
2.1 What do you understand by the term Software Development Life Cycle
(SDLC)? Why is it important to adhere to a life cycle model while
developing a large software product?
2.2 What is software life cycle? Discuss the generic waterfall model.
2.3 List the advantages of using waterfall model instead of adhoc build and
fix model.
2.4 Discuss the prototyping model. What is the effect of designing a
prototype on the overall cost of the project?
2.5 What are the advantages of developing the prototype of a system?
2.6 Describe the type of situations where iterative enhancement model might
lead to difficulties.
2.7 Compare iterative enhancement model and evolutionary process model.


46

Exercises
2.8 Sketch a neat diagram of spiral model of software life cycle.
2.9 Compare the waterfall model and the spiral model of software
development.
2.10 As we move outward along with process flow path of the spiral model,
what can we say about software that is being developed or maintained.
2.11 How does “project risk” factor effect the spiral model of software
development.
2.12 List the advantages and disadvantages of involving a software engineer
throughout the software development planning process.
2.13 Explain the spiral model of software development. What are the
limitations of such a model?
2.14 Describe the rapid application development (RAD) model.Discuss each
phase in detail.
2.15 What are the characteristics to be considered for the selection of the life
cycle model?


47

Exercises
2.16 What is the role of user participation in the selection of a life cycle
model?.
2.17 Why do we feel that characteristics of requirements play a very
significant role in the selection of a life cycle model?
2.18 Write short note on “status of development team” for the selection of a
life cycle model?.
2.19 Discuss the selection process parameters for a life cycle model.
2.20 What is unified process? Explain various phases along with the outcome
of each phase.
2.21 Describe the unified process work products after each phase of unified
process.
2.22 What are the advantages of iterative approach over sequential approach?
Why is unified process called as iterative or incremental?


48

Chapter 2 software development life cycle models

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