SOFTWARE LIFECYCLE MODELS

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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 early70s
• 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
• gt 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 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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SYNCHRONIZE-AND-STABILIZE MODEL

• Microsofts 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 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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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