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CHAPTER 3

Object-Oriented and Classical Software Engineering Fifth Edition, WCB/McGraw-Hill, 2002 Stephen R. Schach srs@vuse.vanderbilt.edu. CHAPTER 3. SOFTWARE LIFE-CYCLE MODELS. Overview. Build-and-fix model Waterfall model Rapid prototyping model Incremental model Extreme programming

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CHAPTER 3

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  1. Object-Oriented and Classical Software EngineeringFifth Edition, WCB/McGraw-Hill, 2002Stephen R. Schachsrs@vuse.vanderbilt.edu

  2. CHAPTER 3 SOFTWARE LIFE-CYCLE MODELS

  3. Overview • 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

  4. Software Life-Cycle Models • 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

  5. Build and Fix Model • Problems • No specifications • No design • Totally unsatisfactory • Need a life-cycle model • “Game plan” • Phases • Milestones

  6. Waterfall Model • Characterized by • Feedback loops • Documentation-driven • Advantages • Documentation • Maintenance easier • Disadvantages • Specification document • Joe and Jane Johnson • Mark Marberry

  7. Rapid Prototyping Model • Linear model • “Rapid”

  8. Three Key Points • Do not turn the rapid prototype into the product • Rapid prototyping may replace the specification phase—never the design phase • Comparison: • Waterfall model—try to get it right the first time • Rapid prototyping—frequent change, then discard

  9. Waterfall and Rapid Prototyping Models • Waterfall model • Many successes • Client’s needs • Rapid prototyping model • Not proved • Has its own problems • Solution • Rapid prototyping for the requirements phase • Waterfall model for the rest of the life cycle

  10. Incremental Model • Divide project into builds

  11. Incremental Model (contd) • Waterfall, rapid prototyping models • Operational quality complete product at end • Incremental model • Operational quality portion of product within weeks • Less traumatic • Smaller capital outlay, rapid return on investment • Need open architecture—maintenance implications • Variations used in object-oriented life cycle

  12. Incremental Model (contd) • Problems • Build-and-fix danger • Contradiction in terms

  13. Incremental Model (contd) • More risky version—pieces may not fit • CABTAB and its dangers

  14. Extreme Programming • 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 a task are drawn up first • Pair programming • Continuous integration of tasks

  15. Unusual Features of XP • Computers are put in the center of a large room lined with cubicles • A client representative is always present • Cannot work overtime for 2 successive weeks • No specialization • Refactoring

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

  17. Synchronize-and Stabilize Model • 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

  18. Synchronize-and Stabilize Model (contd) • 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 the operation of the product

  19. Spiral Model • Simplified form • Waterfall model plus risk analysis preceding each phase

  20. Simplified Spiral Model • View of spiral

  21. A Key Point of the Spiral Model • If all risks cannot be resolved, the project is immediately terminated

  22. Full Spiral Model • Precede each phase by • Alternatives • Risk analysis • Follow each phase by • Evaluation • Planning of next phase • Radial dimension: cumulative cost to date • Angular dimension: progress through the spiral

  23. Full Spiral Model (contd)

  24. Analysis of Spiral Model • Strengths • It is easy to judge how much to test • No distinction is made between development, maintenance • Weaknesses • For large-scale software only • For internal (in-house) software only

  25. Object-Oriented Life-Cycle Models • Need for iteration within and between phases • Fountain model • Recursive/parallel life cycle • Round-trip gestalt • Unified software development process • All incorporate some form of • Iteration • Parallelism • Incremental development • Danger • CABTAB

  26. Fountain Model • Overlap (parallelism) • Arrows (iteration) • Smaller maintenance circle

  27. Conclusions • Different life-cycle models • Each with its own strengths • Each with its own weaknesses • Criteria for deciding on a model include: • 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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