software system engineering chp2

8/13/2019 Software System Engineering Chp2

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ChapterSoftware Development Models

SOFTWARE SYSTEM

ENGINEERING (260CT)


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Motivation/Objective

To distinguish the differences from

another model to another

To understand the importance ofprocess in the development of software.


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Software Development Models

Software lifecycle modelsidentify the

key activitiesin the development of a

software system and their relationships

to one another.


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Models discussed: Linear Sequential Model/Waterfall Model

Prototyping

RAD Model

Evolutionary Software Process Models

The Incremental Model The Spiral Model The WINWIN Spiral Model The Component Assembly Model The Concurrent Development Model


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Linear Sequential/Waterfall

Model

The Waterfall Modelwas originally developed in theearly 1970s in an attempt to provide some structure tolarge-scale software development

The mother of all software engineering models Divided into distinct phases

Recognizes the importance of backtracking (feedback)and iteration in the software process


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Linear Sequential/Waterfall Model

Problem encountered:

Real projects rarely follow the sequential flow

that the model proposed It is often difficult for the customer to state all

the requirement explicitly

The customer must have patience


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Advantages

It is easy to identify milestones

It is easy to separate one stage from another


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Disadvantages

Implies that any stage should be frozen before continuingwith the later stages (resulting in premature requirements,design, coding etc)

Assumes that user requirements can be preciselyspecified.

Requires customer to be patient as no way they canassessing how far the development process has got untilthey sees the nearly-finished product

Unrealistic.


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Suitable for unclear projects.

Pros:

identifying requirements users get a feeling for the system

developers get to "do something"

Cons:

customer demands working product too early

bad solutions will remain: throw-away or not?

Prototyping


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Definition

Limited, working version of a system

under development


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Prototyping Paradigm


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Types of prototyping

Evolutionary prototyping

Throw-away prototyping


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Evolutionary Prototyping

Starts with those requirements that are

well understood


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Throw away prototyping

Starts with those requirements that are

poorly understood


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Prototyping techniques

High level languages

Executable specification languages

Composition of reusable components

Application generators and forth-

generation languages


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Advantages of prototyping

Changing the system early in its

development

Scrapping undesirable systems Designing a systems for users needs

and expectations


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Disadvantages of prototyping

Managing the project

Adopting an incomplete system as

complete


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RAD Model

Suitable for projects with low technical risks

Emphasize on an extremely short development cycle.

RAD is a methodology for compressing the analysis, design,build, and test phases into a series of short, iterative

development cycles

Pros:

Speed.

Reuse.

Cons:Requires many developers.

Requires committed developers.


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RAD Modelcont


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Evolutionary Software Process

Models

The Incremental Model

The Spiral Model

WINWIN Spiral Model

The Component Assembly Model

The Concurrent Development Model


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The Incremental Model

Suitable for products that can be developed in increments.

Combines elements of linear sequential model with the iterativephilosophy of prototyping

Pros: resolves changing/unclear requirements

possible to meet business deadlines with little staff

management of technical risks

Cons: untried?

building in bad solutions


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The Incremental Modelcont


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The Spiral Model

Suitable for large-scale projects.

Pros:

prototyping at any stage

risk reduction as risk analysis is performedat each phase of system development

Increases the quality of the softwaredeveloped

Cons:suitable for internal or in-house

development of large software

risk assessment expertise required


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The Spiral Model


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WINWIN Spiral Model

Extension from Spiral Model

Evolutionary and risk-driven

Anchor points as milestones

Theory WMake everyone a winner

Stakeholders

Customers and Users Developers, maintainers and contractors

Management and investors Achieving WINWIN

Negotiation and Prioritization


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WINWIN Spiral Model


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The Component Assembly

Model

Suitable for component-based technologies such as OO.

Pros:

software reuse

reductions in cycle time

lower project costs

Cons:

Finding components

Are components reusable?

Adaptation


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The Component Assembly Model


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Suitable for all types of projects - "this is how it works

anyhow."

Pros:

Provides both process visibility and

concurrent phases

Cons:

Complicated to keep track of - requirestools.


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Unified Software

Development Process

Developed by the team that createdUML

Embodies best practice in systemdevelopment

Adopts an iterative approach with fourmain phases

Different tasks are captured in a seriesof workflows


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Best Practice

Iterative and incremental development

Component-based development

Requirements-driven development

Configurability

Architecture-centrism

Visual modelling techniques


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Four Phases

Inception

Elaboration

Construction

Transition


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Phases, Workflows

and Iterations

Within each phase activities are grouped

into workflows

The balance of effort spent in eachworkflow varies from phase to phase

Within phases there may be more than

one iteration


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Size of square

relative to time

spent on

workflowh

Inception Elaboration Construction TransitionProject

Phases

1 2 3 4 5 6 7 8

Iterations within

each phaseRequirements

nalysis

Design

Implementation

Test

Workflows


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Difference from

Waterfall Life Cycle

In a waterfall life cycle project the phases andthe workflows are linked together

In the Requirements phase, only Requirementsworkflow activities are carried out

All Requirements activity should be completedbefore work starts on Analysis

In an iterative life cycle project it is recognisedthat some Requirements work will behappening alongside Analysis work


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Requirements

nalysis

Design

Implementation

Test

Requirementsnalysis

DesignImplementation

Test


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Major Activities of the

Development Process

Activity Techniques Key Deliverables

Requirements

Capture andModelling

Requirements

ElicitationUse Case

Modelling

Prototyping

Use Case Model

Requirements ListPrototypes

Glossary


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Development Process


Requirements

Analysis

Collaboration

DiagramsClass and Object

Models

Analysis

Modelling

Analysis Models


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Development Process


System

Design

Deployment

ModellingComponent

Modelling

Package

ModellingArchitectural

Modelling

Overview Design

andImplementation

Architecture


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Development Process


Class Design Class and Object

ModellingInteraction

Modelling

State Modelling

Design Patterns

Design Models


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Development Process


User

InterfaceDesign

Class and Object

ModellingInteraction Modelling

State Modelling

Package Modelling

Prototyping

Design Patterns

Design Models

with InterfaceSpecification


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Development Process


Data

ManagementDesign

Class and Object

ModellingInteraction

Modelling

State Modelling

PackageModelling

Design Patterns

Design Models

with DatabaseSpecification


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Development Process


Construction Programming

Component Re-use

Database DDL

Programming

Idioms

Constructed

SystemDocumentation

software system engineering chp2

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