uhd-cs3320-c031 software life-cycle models cs 3320--chapter 3
TRANSCRIPT
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SOFTWARE LIFE-CYCLE MODELS
CS 3320--Chapter 3
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MODELS• Build-And-Fix Model• Waterfall Model• Rapid Prototyping Model• Incremental Model• Spiral Model• Object-Oriented Model
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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
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WATERFALL MODEL• First developed by Royce in early70’s• Documentation Driven• Verification/Test at each phase• Feedback loops
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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
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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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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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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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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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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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ANALYSIS OF THE INCREMENTAL MODELProblems:• 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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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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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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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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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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ANALYSIS OF SPIRAL MODELRestrictions:• 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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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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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