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TCS2411 Software Engineering 1

Software Life Cycle

What happens in the life of software

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TCS2411 Software Engineering 2

Lecture Objectives

To look at the life cycle of a software

To understand the software process andits related elements

To relate to the different softwareengineering paradigms

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TCS2411 Software Engineering 3

Software Engineering

Layers

a quality focusa quality focus

process modelprocess model

methodsmethodstoolstools

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TCS2411 Software Engineering 4

Software Process

Activities in software projects

Characterised by a common processframework

Framework activities - task sets

Umbrella activities

Process maturity enables developmentof quality software products

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TCS2411 Software Engineering 5

Common Process

Framework

Common process frameworkCommon process framework

Framework activitiesFramework activities

work taskswork tasks

work productswork products

milestones & deliverablesmilestones & deliverables

QA checkpointsQA checkpoints

Umbrella ActivitiesUmbrella Activities

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TCS2411 Software Engineering 6

Umbrella Activities

Software project management Formal technical reviews S

oftware quality assurance Software configuration management Document preparation and production Reusability management

Measurement Risk management

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TCS2411 Software Engineering 7

Process as Problem

Solving

statusquo

problemdefinition

technicaldevelopment

solution

integration

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TCS2411 Software Engineering 8

The Process Model:

Adaptability

the framework activities will alwaysbe applied on every project ... BUT

the tasks (and degree of rigor) foreach activity will vary based on: the type of project (an entry point to

the model)

characteristics of the project

common sense judgment; concurrenceof the project team

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TCS2411 Software Engineering 9

The Primary Goal:

High Quality

Remember:Remember:

High quality = project timelinessHigh quality = project timeliness

Why?Why?

Less rework!Less rework!

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TCS2411 Software Engineering 10

The Systematic Process

Problem

Models

Solution

Analysis

Design

Development

Testing

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TCS2411 Software Engineering 11

Generic Phases

Definition Phase

Focus on what the software is

Development Phase

Focus on how the software works

Maintenance Phase

Focus on change to the software

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TCS2411 Software Engineering 12

Definition Phase

Identify information to be processed

Identify system behaviour - functions and

performance Determine constraints, interfaces,

validation criteria

Major tasks:

System engineering

Software project planning

Requirements analysis

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TCS2411 Software Engineering 13

Development Phase

Define data structures, functionimplementation, procedural details, interfaces

Translate design to programming language

How testing is performed

Major tasks:

Software design

Code generation

Software testing

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TCS2411 Software Engineering 14

Maintenance Phase

Reapplies definition and developmentphases to existing software

Types of changes:

Correction

Adaptation

Enhancement Prevention

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TCS2411 Software Engineering 15

Waterfall Model

SystemEngineering

Analysis

Design

Code

Testing

Maintenance

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TCS2411 Software Engineering 16

Waterfall Model

Characteristics

The classic life cycle - oldest and mostwidely used paradigm

Activities flow from one phase to another

If there are corrections, return to aprevious phase and flow from there again

Major advantages: Good for planning andwell-defined/repeated projects

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TCS2411 Software Engineering 17

Problems ofWaterfall

Model

Real projects often follow the sequence

All requirements may not be stated

explicitly by customer

Customer only sees the results after sometime

Developers are often delayed at certainphases

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TCS2411 Software Engineering 18

Prototyping Model

Stop

Requirements

gathering and

refinement

Building

prototype

Quick

design

Customer

evaluation

Refining

prototype

Engineer

product

Start

listento

customer

build/revisemock-up

customertest-drivesmock-up

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TCS2411 Software Engineering 19

Prototyping Model

Characteristics

Developer and customer determineobjectives and draft requirements

Prototype quickly produced and evaluatedby customer

Prototype then refined, and re-evaluated

Process iterated, before final productdevelopment

Advantages: Customer participation andbetter requirements

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TCS2411 Software Engineering 20

Problems of Prototyping

Model

Problem 1: Customer may see prototypeas working model and expects fast results

Problem 2: Developer compromised whenproducing prototype quickly, e.g. differentoperating system or programming

language

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TCS2411 Software Engineering 21

Rapid Application

Development (RAD)

Business

Modeling

DataModeling

Process

ModelingApplication

GenerationTesting &

Turnover

Team #1 BusinessModeling

Data

ModelingProcess

ModelingApplication

GenerationTesting &

Turnover

Team #2

Time period

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TCS2411 Software Engineering 22

RAD Characteristics

High-speed version of waterfall model

Primarily for information systems applications

Requirements well-understood, fully functionalsystem produced in short time

The application modularised - major functionscan be completed in 3 months

Separate teams complete the functions, thenintegrated as a whole

Requires human resource and commitment

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TCS2411 Software Engineering 23

Incremental Model

analysis design code test

System/informationengineering

analysis design code test

analysis design code test

analysis design code test

increment 2

increment 3

increment 4

increment 1

delivery of1st increment

delivery of2nd increment

delivery of

3rd increment

delivery of4th increment

calendar time

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TCS2411 Software Engineering 24

Incremental Model

Characteristics

Software separated into differentincrements - complete working portions

Focus on delivery of operational productwith each increment - can be evaluated

Useful when insufficient staff and can be

planned to manage technical risks, e.g.waiting for new hardware

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TCS2411 Software Engineering 25

Spiral Model

Customer

Communication

Planning

Construction & ReleaseCustomerEvaluation

Engineering

Risk Analysis

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TCS2411 Software Engineering 26

Spiral Model

Characteristics

Originally proposed by Boehm, couplesiterative nature of prototyping and the

systematic aspects of waterfall model Software is developed in series of

incremental releases

Each iteration produces a more completeproduct

Better management through risk analysis

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TCS2411 Software Engineering 27

Problems of Spiral

Model

May be difficult to convince customersthat evolution is controllable

Demands risk assessment expertise -major risk will cause problems if notidentified

Relatively new and not widely used -cannot determine performance

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TCS2411 Software Engineering 28

Component Assembly

Model

Identify

candidate

components

Look up

components

in library

Available?

Extract

components

Build

components

Construct

System

yes

no

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TCS2411 Software Engineering 29

Component Assembly

Characteristics

Use of object-oriented technology

Components - classes that encapsulate

both data and algorithms

Components developed to be reusable

Paradigm similar to spiral model, but

engineering activity involves components

System produced by assembling thecorrect components

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TCS2411 Software Engineering 30

Fourth Generation

Techniques (4GT)

"

Design"

Strategy

Testing

Requirementsgathering

Implementationusing 4GL

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TCS2411 Software Engineering 31

4GT Characteristics

Use of software tools that allow softwareengineer to specify s/w characteristics athigher level

The tools generate codes based onspecification

More time in design and testing - increase

productivity

Tools may not be easy to use, codesgenerated may not be efficient

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TCS2411 Software Engineering 32

Other Process Models

Component assembly modelthe process toapply when reuse is a development objective

Concurrent process model

recognizes thatdifferent part of the project will be at differentplaces in the process

Formal methodsthe process to apply when amathematical specification is to be developed

Cleanroom software engineeringemphasizes error detection before testing

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TCS2411 Software Engineering 33

Conclusion

The paradigm used for development ofsoftware depends on a number of factors People - staff & users

Software product Tools available

Environment

Existing models makes developmentprocess clearer, but they can be evolvedto become new paradigms

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TCS2411 Software Engineering 34

References

Software Engineering: APractitionersApproach 5th Ed. by Roger S. Pressman,Mc-Graw-Hill, 2001

Software Engineering by Ian Sommerville,Addison-Wesley, 2001