Software Engineering Zhang Shuang

Chapter 9 Software Life-cycle Models Software Life-cycle Models Zhang Shuang,

Software Life-Cycle Models Life-cycle model, the series of steps through which the product progresses The life-cycle of each product is different:  Software size  Software type  Development environment & technique Use the suitable model for each product Zhang Shuang,

Software Life-Cycle Models  Different life-cycle models:  Build-and-fix model  Waterfall model  Rapid prototyping model  Incremental model  Synchronize-and-stabilize model  Spiral Model  Fountain model Zhang Shuang,

1. Build and Fix Model Problems  No specifications  No design Totally unsatisfactory Need a life-cycle model  “Game plan”  Phases  Milestones Zhang Shuang,

2. Waterfall Model Characterized by  Feedback loops  Documentation-driven Advantages  Documentation  Maintenance easier Disadvantages  Specification document Widely used before 80s

3. Rapid Prototyping Model Linear model “Rapid”

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 Zhang Shuang,

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 Zhang Shuang,

4. Incremental Model  Divide project into builds

4. Incremental Model  Advantages:  The complete product is divided into builds and the developer delivers the product build by build.  It reduces the traumatic effect of imposing a completely new product on the client organization.  From the client’s financial viewpoint, phased delivery requires no large capital outlay. Zhang Shuang,

4. Incremental Model  Problems  Build-and-fix danger  Contradiction in terms Zhang Shuang,

5. 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 Zhang Shuang,

5. Synchronize-and-Stabilize Model  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 Zhang Shuang,

6. Spiral Model  Simplified form  Waterfall model plus risk analysis preceding each phase

Simplified Spiral Model  View of spiral

A Key Point of the Spiral Model  If all risks cannot be resolved, the project is immediately terminated Zhang Shuang,

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 Zhang Shuang,

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 Zhang Shuang,

7 Fountain Model  Overlap (parallelism)  Arrows (iteration)  Smaller maintenance circle

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 Zhang Shuang,

9 Software Life-Cycle Models  Note that there is no  Planning Phase  Testing Phase  Documentation Phase  These are ongoing constant processes Zhang Shuang,