7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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SOFTWARE ENGINEERING -SOFTWARE LIFECYCLE MODELS

• These slides contain a few different software lifecycle models.

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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THE BASIC WATERFALL MODEL

Requirement specification

Maintenance

Testing

Implementation

Analysis & Design

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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A MODIFIED WATERFALL MODEL

Requirement spec. - V&V

Maintenance

- V&V

Testing - V&V

Implementation

- V&V

Analysis & Design - V&V

V&V = Verification and Validation

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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PROTOTYPING FOR REQUIREMENT ANALYSIS

Requirement spec. - V&V

Maintenance

- V&V

Testing - V&V

Quick Implementa-tion - V&V

Analysis & Design - V&V

V&V = Verification and Validation

Quick Analysis & Design - V&V

Implementation

- V&V

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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THE SPIRAL (ITERATIVE) MODEL

A0

A1

D1 C1

B0

B1

A2 B2

D2

D3

C2

C3

PlanningRisk analysisPrototyping

Client evaluationand input

Model simulationOperational prototypeVerification for next level

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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INCREMENTAL SOFTWARE DEVELOPMENT

• It is useful to divide the development so that the subsequent releases are based on the previous releases.

• Here it is important to choose the increments in such a way, that the feedback from the previous increments shows if the development is going right.

• Also, the previous releases should be independent of the following ones.

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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EVOLUTIONARY SOFTWARE DEVELOPMENT

• In evolutionary software development different activities (design, implementation, testing, and even requirements specification) may all progress at the same time.

• In this type of a situation controlling the project can be very difficult.

• Evolutionary software development may take place because it is not really known what is needed or how it can be achieved.

• Evolutionary software development may also be a sign of lack of control over the development process.

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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THE MANAGEMENT VIEW

Maintenance and audit

Installation

Build new system: requirement specification, analysis & design, implementation, testing

Do a feasibility study to find out whether it is feasible to implement a new system.

7.1.2003 Software Engineering 2004Jyrki Nummenmaa

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NEW DEVELOPMENTS

• Special considerations for distributed software and web-based software

• Availability of Commercial Off-The-Shelf (COTS) components.

• Many companies now work as integrators – they use COTS and subcontractors and maybe only write a minor part of the software themselves.

• “Lightweight” process models to get more flexibility and to aknowledge the fact that it is so hard to get the requirements right.