1. SOFTWARE LIFE-CYCLE MODELS
CS Chapter 3
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2. MODELS Build-And-Fix Model Waterfall Model Rapid Prototyping Model
Incremental Model
Spiral Model
Object-Oriented Model
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4. BUILD-AND-FIX MODEL No Specifications No design Reworked many times
Totally unsatisfactory
Need life-cycle model
“Game Plan”
Phases
Milestones
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5. WATERFALL MODEL First developed by Royce in early70’s
Documentation Driven
Verification/Test at each phase
Feedback loops
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7. ANALYSIS OF THE WATERFALL MODEL
Advantages
Enforced discipline
documentation-driven model
testing by SQA
Maintenance easier
Disadvantages
Requirements & Spec Analysis
graphical aids are used
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8. RAPID PROTOTYPING MODEL
Rapid Prototype used for requirements and specifications analysis.
Rapid Prototype contains a subset of the functionality of the target product
Structure of prototype not important, but speed of development process is--RAPID
Prototype can be used in requirement phase of WF model
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10. RAPID PROTOTYPING MODEL cont.
Advantages
Helps get requirements right
Good insight to estimate budget and time requirements
Help in design phase
==> less feedback loops
Disadvantages
Prototype adds to the cost (overall it may reduce cost)
Temptation to turn prototype into product
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11. RAPID PROTOTYPING MODEL cont.
Key points
Do not turn it into product
Prototype may replace requirement phase but never the design phase
Waterfall model-- try to get right the first time
Rapid Prototype-- Allows better feedback from client at earliest stage of the process.
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12. INCREMENTAL MODEL The product is constructed step by step
The product is divided into a series of incremental builds
Each build consist of a set of module that provide a functionality
Product provided to client build by build
Each new build is integrated with previous builds and delivered to client
Production may stop at end of any build
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14. ANALYSIS OF THE INCREMENTAL MODEL
Waterfall: operational quality of complete product at end
Incremental model: deliver operational quality of portion of product in “short” time
Reduces the effect of introducing a new system on users: less traumatic
Smaller capital outlay
The process can be stopped at end of any build
Need open architecture-- good for maintenance
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15. ANALYSIS OF THE INCREMENTAL MODEL
Problems:
If broken into too few builds then it degenerates into the build-and-fix model
If broken into too many builds then integration of the builds can turn out to be too costly.
Note: Requirements, Specs and Design are done for whole product. Only Implementation and Integration are incremental.
A more risky version: incremental Specs and Design
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17. SYNCHRONIZE-AND-STABILIZE MODEL
Microsoft’s life-cycle model
Requirements analysis--interview potential customers
Draw up specifications
Divide project into 3 to 4 builds
Each build carried out by small teams working in parallel
At end of each day--Synchronize (integrate modules into build, test & debug)
At end of each build-Stabilize (freeze build)
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18. SPIRAL MODEL Simplified form Waterfall model plus risk analysis
Precede each phase by
Alternatives
Risk analysis: performance, budget, milestones
Follow each phase by
Evaluation
Planning of next phase
Prototypes may be used to analyze risks
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20. SPIRAL MODEL Refer to Figure
radial dimension shows cumulative cost to date
Angular dimension shows progress through the spiral
Each cycle corresponds to a phase
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22. ANALYSIS OF SPIRAL MODEL
Advantages:
It is a risk-driven model
Risk analysis highlights the need to stay within budget, on schedule and quality assurance.
If risks can not be resolved, terminate project
No distinction between development and maintenance.
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23. ANALYSIS OF SPIRAL MODEL
Restrictions:
Intended for internal (in-house) software
Contract software: risk analysis can not be done at each phase.
Applicable to only large-scale software
cost of risk analysis
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24. OBJECT-ORIENTED MODELS
Intended to overcome shortcomings of previous models
Emphasis on incorporating
iterations, refinement, and feedback
overlap and parallelism between phases
incremental development
Danger
Can degenerate into CABTAB (Code A Bit Test A Bit)
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26. CONCLUSION Different life-cycle models Build-and-Fix should be avoided
WF: well known with strengths and weaknesses
Rapid-Prototype: strengthens WF model
Incremental model
Synchronize-and-Stabilize: used with success by Microsoft
Spiral: risk analysis driven
Best suggestion: “Mix-and-match” life-cycle
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