SOFTWARE LIFE-CYCLE MODELS CS 3320--Chapter 3 UHD-CS3320-C03

MODELS Build-And-Fix Model Waterfall Model Rapid Prototyping Model Incremental Model Spiral Model Object-Oriented Model UHD-CS3320-C03

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BUILD-AND-FIX MODEL No Specifications No design Reworked many times Totally unsatisfactory Need life-cycle model “Game Plan” Phases Milestones UHD-CS3320-C03

WATERFALL MODEL First developed by Royce in early70’s Documentation Driven Verification/Test at each phase Feedback loops UHD-CS3320-C03

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ANALYSIS OF THE WATERFALL MODEL Advantages Enforced discipline documentation-driven model testing by SQA Maintenance easier Disadvantages Requirements & Spec Analysis graphical aids are used UHD-CS3320-C03

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 UHD-CS3320-C03

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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 UHD-CS3320-C03

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. UHD-CS3320-C03

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 UHD-CS3320-C03

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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 UHD-CS3320-C03

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 UHD-CS3320-C03

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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) UHD-CS3320-C03

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 UHD-CS3320-C03

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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 UHD-CS3320-C03

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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. UHD-CS3320-C03

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 UHD-CS3320-C03

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) UHD-CS3320-C03

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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 UHD-CS3320-C03