SOFTWARE LIFE-CYCLE MODELS

Slide 3.1 © The McGraw-Hill Companies, 2002 CHAPTER 3 SOFTWARE LIFE-CYCLE MODELS...

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CHAPTER 3

SOFTWARE LIFE-CYCLE MODELS

© The McGraw-Hill Companies, 2002

Slide 3.1

Overview z z z z z z z z z

Build-and-fix model Waterfall model Rapid prototyping model Incremental model Extreme programming Synchronize-and-stabilize model Spiral model Object-oriented life-cycle models Comparison of life-cycle models

© The McGraw-Hill Companies, 2002

Slide 3.2

Software Life-Cycle Models z z

Life-cycle model (formerly, process model) The steps through which the product progresses – – – – – – –

Requirements phase Specification phase Design phase Implementation phase Integration phase Maintenance phase Retirement

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Slide 3.3

Build and Fix Model z

Problems – No specifications – No design

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Totally unsatisfactory Need life-cycle model – “Game plan” – Phases – Milestones

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Slide 3.4

Waterfall Model (contd) z

Characterized by – Feedback loops – Documentation-driven

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Advantages – Documentation – Maintenance easier

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Disadvantages – Specifications » Joe and Jane Johnson » Mark Marberry

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Rapid Prototyping Model z z

Linear model “Rapid”

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Slide 3.6

Three Key Points z z

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Do not turn into product Rapid prototyping may replace specification phase—never the design phase Comparison: – Waterfall model—try to get it right first time – Rapid prototyping—frequent change, then discard

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Slide 3.7

Waterfall and Rapid Prototyping Models z

Waterfall model – Many successes – Client needs

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Rapid prototyping model – Not proved – Has own problems

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Solution – Rapid prototyping for requirements phase – Waterfall for rest of life cycle

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Slide 3.8

Incremental Model z

Divide project into builds

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Incremental Model (contd) z

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Waterfall, rapid prototyping models – Operational quality complete product at end

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Incremental model – Operational quality portion of product within weeks

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Less traumatic Smaller capital outlay, rapid return on investment Need open architecture—maintenance implications Variations used in object-oriented life cycle

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Incremental Model (contd) z

Problems – Build-and-fix danger – Contradiction in terms

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Slide 3.11

Incremental Model (contd) z

More risky version—pieces may not fit – CABTAB and its dangers

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Slide 3.12

Extreme Programming z z z z z z z z

Somewhat controversial new approach Stories (features client wants) Estimate duration and cost of each story Select stories for next build Each build is divided into tasks Test cases for task are drawn up first Pair programming Continuous integration of tasks

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Slide 3.13

Unusual Features of XP z

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Computers are put in center of large room lined with cubicles Client representative is always present Cannot work overtime for 2 successive weeks No specialization Refactoring

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Evaluating XP z z

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XP has had some successes Good when requirements are vague or changing Too soon to evaluate XP

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Slide 3.15

Synchronize-and Stabilize Model z z

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Microsoft’s life-cycle model Requirements analysis—interview potential customers Draw up specifications Divide project into 3 or 4 builds Each build is carried out by small teams working in parallel

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Synchronize-and Stabilize Model (contd) z

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At the end of the day—synchronize (test and debug) At the end of the build—stabilize (freeze build) Components always work together – Get early insights into operation of product

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Spiral Model z

Simplified form – Waterfall model plus risk analysis

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Precede each phase by – Alternatives – Risk analysis

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Follow each phase by – Evaluation – Planning of next phase © The McGraw-Hill Companies, 2002

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Simplified Spiral Model z

If risks cannot be resolved, project is immediately terminated

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Full Spiral Model z z

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Radial dimension: cumulative cost to date Angular dimension: progress through the spiral

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Full Spiral Model (contd)

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Slide 3.21

Analysis of Spiral Model z

Strengths – Easy to judge how much to test – No distinction between development, maintenance

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Weaknesses – For large-scale software only – For internal (in-house) software only

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Slide 3.22

Object-Oriented Life-Cycle Models z

Need for iteration within and between phases – – – –

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Fountain model Recursive/parallel life cycle Round-trip gestalt Unified software development process

All incorporate some form of – Iteration – Parallelism – Incremental development

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Danger – CABTAB © The McGraw-Hill Companies, 2002

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Fountain Model z z

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Features Overlap (parallelism) Arrows (iteration) Smaller maintenance circle

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Slide 3.24

Conclusions z z z z

Different life-cycle models Each with own strengths Each with own weaknesses Criteria for deciding on a model include – – – –

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The organization Its management Skills of the employees The nature of the product

Best suggestion – “Mix-and-match” life-cycle model

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