Software Project Management

Software Project Management

Lecture 2Software Development Models

Software project management 2

Overview Introduction Technical plan Software process models Selecting process model(s)


Definitions Software Process

the set of activities, methods, and practices that are used in the production and evolution of software

Software Process Model one specific embodiment of a

software process architecture(Humphrey 1990)


Why Modelling? To provide a common understanding To locate any inconsistencies,

redundancies and omissions To reflect the development goals

and provide early evaluation To assist the development team to

understand any special situation


Project Analysis Methodologies

Object-Oriented Development (OOD) Structured System Analysis and

Design Method (SSADM) Jackson Structured Programming (JSP)

Technologies application-building environments knowledge-based system tools


Project Characteristics data oriented or control oriented

system? general package or application

specific? a particular type of system for which

specific tools have been developed? safety-critical system? nature of the hardware/software

environment?


Project Risks Product uncertainty Process uncertainty Resource uncertainty


Considerations for Project Approach Control systems Information systems General applications Specialized techniques Hardware environment Safety-critical systems Imprecise requirements


Technical Plan Contents

Constraints Approach Implementation Implications


Technical Plan - Constraints Character of the system to be

developed Risks and uncertainties of the

project User requirements concerning

implementation


Technical Plan - Approach Selected methodology or process

model(s) Development methods Required software tools Target hardware/software

environment


Technical Plan - Implementation Development environment Maintenance environment Training


Technical Plan - Implications Project products and activities

effect on schedule duration and overall project effort

Financial report used to produce costings


Software Process Models Waterfall Model V Model Spiral Model Prototyping Model


Software Process Models (cont’d) Phased Development Model

incremental development model iterative development model

Operational Specification Model Transformation Model


Waterfall ModelRequiremen

tsAnalysis

SystemDesign

Coding

TestingMaintenanc

e


Waterfall Model (cont’d) classical one-shot approach effective control limited scope of iteration long cycle time not suitable for system of high

uncertainty


V ModelRequirements Analysis

System Design

Program Design

Coding

Unit andIntegration

Testing

System Testing

Maintenance

User Acceptance

Testing


V Model (cont’d) Additional validation process

introduced Relate testing to analysis and

design Loop back in case of discrepancy


Spiral Model (adapted from Boehm 1987)

Plan next phases

Determine objectives, alternatives and constraints

Evaluate alternatives; identify and resolve risks

Develop and verify next-level

product

Requirements plan

Development plan

Integration and Test

plan

Concept of operation

Risk analysis

Risk analysis

Risk analysis

PrototypePrototypePrototype

Software requirements

Requirements validation

System product design

Design validationAcceptance test

Integration and Test

Unit testing

Coding

Detailed design

Cumulative costProgress through steps


Spiral Model (cont’d) Evolutionary approach Iterative development combined

with risk management Risk analysis results in “go, re-do,

no-go” decision


Spiral Model (cont’d) Four major activities

Planning Risk analysis Engineering Evaluation


Prototyping Model Goals

meet (some) user requirements at an early stage

reduce risk and uncertainty verify a design or implementation

approach Should always answer specific

questions; goals must be identified


Classification of Prototype Throw-away

After users agree the requirements of the system, the prototype will be discarded.

Evolutionary Modifications are based on the existing

prototype. Incremental

Functions will be arranged and built accordingly.


Prototyping Model

Build prototype Usersatisfaction

YES

NOUser feedback


Benefits of Prototyping Learning by doing Improved communication Improved user involvement Clarification of partially-known

requirements


Prototyping Sequences Requirements gathering Quick design Prototype construction Customer evaluation Refinement Loop back to quick design for fine

tuning Product engineering


Benefits of Prototyping Demonstration of the consistency

and completeness of a specification Reduced need for documentation Reduced maintenance costs Feature constraint Production of expected results for

testing real system


Drawbacks of Prototyping Users sometimes misunderstand

the role of the prototype Lack of project standards possible Lack of control Additional expense Machine efficiency Close proximity of developers


Forms of Prototypes Mock-ups Simulated interaction Partial working model


Prototype Products Human-computer interface System functionality


Prototype Changes Three categories

Cosmetic (35%) screen layout

Local (60%) screen processing

Global (5%) multi-parts processing design review


Phased Development Reduce cycle time Two parallel systems:

operational system (Release n) development system (Release n+1)

Two approaches incremental iterative


Incremental Model Break system into small

components Implement and deliver small

components in sequence Every delivered component

provides extra functionality to user


Incremental Model (cont’d)Requirements Analysis

Arrange requiremen

ts in increments

Validate increme

nt

Design and develop

increment

Integrate incremen

tYES

NOSystem

OK?


Iterative Model Deliver full system in the

beginning Enhance functionality in new

releases


Iterative Model (cont’d)

Develop system

version n

Validate system

version n

YES

NODesign system

version n

Systemcomplete

n = n+1


Combined Incremental and Iterative Model Every new release includes

extra functionality enhancement of existing functionality

Popularly used in software industry


Ranking the Increments Rank by value to cost ratio V = value to customer (score 1 -

10) C = cost (score 1- 10) Value to cost ratio = V/C Example: Table 4.1


Advantages of Phased Development Early feedback Less possible requirement changes Early benefits for users Improved cash flow Easier to control and manage


Advantages of Phased Development (cont’d) Capture early market Facilitate early training Can be temporarily abandoned Increase job satisfaction


Disadvantages of Phased Development ‘Software breakage’ Reduced productivity


Operational Specification Model Executable or translatable

specification Use executables to demonstrate

system behaviour Resolve requirement uncertainties in

early stage Merging functionality and system

design


Transformational Model Transform a specification into

delivered system Requires automated support Relies on formal specification

method


References Boehm, B. (1987) A sprial model of software

development and enhancement, Software Engineering Project Management, p.128–142.

Hughes, B. and Cotterell, M. (1999) Software Project Management, 2nd ed., McGraw Hill.

Humphrey, W. (1990) Managing the Software Process, Addison-Wesley.

Pfleeger, S.L. (1998) Software Engineering Theory and Practice, Prentice Hall

Software Project Management

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