S/W Project Management Software Process Models. Objectives To understand Software process and process models, including the main characteristics of.

S/W Project Management

Software Process ModelsSoftware Process Models

Objectives

To understand Software process and process models,

including the main characteristics of each model, critical software process issues, and the pros and cons of each model.

The generic process activities and what they mean. This includes details of what exactly each activity is for and the stages within them.

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The software process

A structured set of activities required to develop a software system Specification; Design; Validation; Evolution.

A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.

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Abstraction

Elimination of unnecessary detail Model

Abstract view Abstract

representation

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Software Process model

A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.

No universal software processHighly intellectualMust dynamically adjust to creative

needs of professionals and tasks

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Critical Software Process Issues

Factors to considerNature of the project.

Software projects are different.Organizational needs.Experience level of members/teamCurrent product status

E.g., Brand new product?Available tools and facilities

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Critical Software Process Issues

Factors to considerQuality

More intensive quality assuranceProduct Technology

New technology or algorithm?Requirements instability

Unknown requirements Unstable requirements

Complexity Large systems

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Software Process Models

WaterfallVSpiralRapid Application Development

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Waterfall model

Requirements

definition

System andsoftware design

Implementationand unit testing

Integration andsystem testing

Operation and

maintenance

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Waterfall model phases

Requirements analysis and definitionSystem and software designImplementation and unit testingIntegration and system testingOperation and maintenanceThe main drawback of the waterfall

model is the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase.

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Waterfall model problems

Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements.

Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process.

Few business systems have stable requirements.

Requirements have to be understood early on. S/W Process Models

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V-Shaped Model

Project and Requirements Planning

Product Requirements and Specification Analysis

Architecture or High-Level Design

Detailed Design

Unit Testing

Integration and Testing

System and Acceptance Testing

Coding

Production Operation and Maintenance

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V-Shaped Model

A variation of the Waterfall model. Places strong emphasis on Verification and

Validation. Testing of the product is planned in the early phases

of the process. Acceptance test plan is developed. System test plan is developed.

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V-Shaped Model

Emphasizes the relationship between the phases preceding and following coding.

The dotted lines indicate that these phases should be considered in parallel.

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Phases in the V-Shaped Model

Project and requirements planning– Determines system requirements and allocation of

resources. Product requirements and specification analysis

– Analysis of software problem, concludes with complete specification of the software.

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Phases in the V-Shaped Model

Architecture or High-level design– Determines how the software functions are to

implement the design. Detailed Design

– Defines algorithms for components that were defined during the architecture phase.

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Phases in the V-Shaped Model

Coding– Transforms the algorithms defined during the design

phase into software. Unit Testing

– Checks each code module for errors.

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Phases in the V-Shaped Model

Integration and Testing– Integrate and test individual code modules.

System and acceptance testing– Test entire software system in its hardware

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Phases in the V-Shaped Model

Productions, operation and maintenance– Puts software into production and provides for

enhancements and corrections.

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V-Shaped Model Problems

Does not easily handle concurrent events

No iteration of phasesCannot handle dynamic changes in

requirements throughout the life cycleRequirements are tested too late to

make changes without affecting the schedule

No risk analysisS/W Process Models

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Spiral development

Process is represented as a spiral rather than as a sequence of activities with backtracking.

Each loop in the spiral represents a phase in the process.

No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required.

Risks are explicitly assessed and resolved throughout the process.

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Spiral model of the software process

Determine objectives, alternatives and constraints

Evaluate alternatives, identify, resolve risks

Develop, verify next-level product

Plan next phaseAnd test plan

requirements

Operational prototype

Riskanalysis

Riskanalysis

Riskanalysis

Riskanalysis Proto-

type 1

Prototype 2

Prototype 3Opera-tionalprotoype

Concept ofOperation

Simulations, models, benchmar ks

S/Wrequirements

Requirementvalidation

DesignV&V

Productdesign Detailed

design

Code

Unit test

IntegrationtestAcceptance

testService

Integrationand test plan

Developmentplan

Requirements planLife-cycle plan

REVIEW

Spiral model sectors

Objective setting Specific objectives for the phase are

identified.Risk assessment and reduction

Risks are assessed and activities put in place to reduce the key risks.

Development and validation A development model for the system is chosen

which can be any of the generic models.Planning

The project is reviewed and the next phase of the spiral is planned.

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Spiral Model problems

Highly dependent on risk analysis Requires very knowledgeable personnel Errors may occur if risk is not properly

analyzedWillingness of the Customer

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RAD Model

Rapid Application DevelopmentUser is involved in all phasesUse tools that allow product evaluation at

all stages of developmentCharacterized by quick turnaround time

from requirements definition to deliveryHigh component reuse factor

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RAD ModelD

evel

opm

ent

Eff

ort

Time

Requirements Planning

User Description

Construction

Cut Over

User Involvement

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Phases in RAD Model

Requirements planning phase– Requirements are gathered using technique called joint

requirements planning (JRP) User description

– Joint application design (JAP) is used to harness user involvement.

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Phases in RAD Model

Construction phase– Combines design, coding, testing. Heavy use of code

generators and other production tools Cut over

– Acceptance testing, installation and user training.

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Strengths of RAD

Use of powerful tools reduces cycle time

Lower cost due to reduced cycle timeOngoing customer involvementReuse of existing program component

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RAD problems

Heavily dependent on user involvement throughout the process.

Requires highly skilled developers in the use of development tools.

Heavily dependent on reusable components.

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Generic activities

SpecificationDesign (and implementation)ValidationEvolution

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Specification

The process of establishing what services are required and the constraints on the system’s operation and development.

Requirements engineering process Feasibility study; Requirements elicitation and analysis; Requirements specification; Requirements validation.

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Example requirements engineering process

Feasibilitystudy

Requirementselicitation and

analysisRequirementsspecification

Requirementsvalidation

Feasibilityreport

Systemmodels

User and systemrequirements

Requirementsdocument

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Design and implementation

The process of converting the system specification into an executable system.

design Design a software structure that realises

the specification;Implementation

Translate this structure into an executable program;

The activities of design and implementation are closely related and may be inter-leaved.

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Example design process activities

Architectural designAbstract specificationInterface designComponent designData structure designAlgorithm design

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Example software design process

Architecturaldesign

Abstractspecification

Interfacedesign

Componentdesign

Datastructuredesign

Algorithmdesign

Systemarchitecture

Softwarespecification

Interfacespecification

Componentspecification

Datastructure

specification

Algorithmspecification

Requirementsspecification

Design activities

Design products

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Validation

Verification and validation (V & V) is intended to show that a system conforms to its specification and meets the requirements of the system customer.

Involves checking and review of processes, various testing stages.

Testing involves executing the system with test cases that are derived from the specification.

Testing tries to establish if observed behaviour matches expected behaviour.

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Testing stages

Unit testing Individual components are tested independently; Components may be functions or objects or coherent

groupings of these entities.Integration testing (subsystem testing)

Individual components are merged and tested.System testing

Testing of the system as a whole. Testing of emergent properties is particularly important.

Acceptance testing Testing with customer data to check that the system

meets the customer’s needs.

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Testing phases

Requirementsspecification

Systemspecification

Systemdesign

Detaileddesign

Module andunit codeand test

Sub-systemintegrationtest plan

Systemintegrationtest plan

Acceptancetest plan

ServiceAcceptance

testSystem

integration testSub-system

integration test

note that model is V

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Evolution

Software is inherently flexible and can change.

As requirements change through changing business circumstances, the software that supports the business must also evolve and change.

Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new.

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Example evolution process

Assess existingsystems

Define systemrequirements

Propose systemchanges

Modifysystems

Newsystem

Existingsystems

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