Software Lifecycle Models

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Software Lifecycle Models

• CSSE 372, Software Project Management
• Mark Ardis, Rose-Hulman Institute
• December 14, 2004

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Outline

• Undisciplined Process Models
• Waterfall Model
• Modified Waterfalls
• Incremental Models
• Spiral
• Evolutionary Prototyping
• Staged Delivery
• Design-to-Schedule
• Evolutionary Delivery
• Other Models

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Undisciplined Process Models

• Ad hoc
• while (project unfinished)
• pick something at random
• work on it
• Build-and-fix
• while (project unfinished)
• write some code
• fix the errors

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Waterfall Model

• Manufacturing life cycle model
• Assumes
• multi-stage development cycle
• completely separate stages
• output of one stage is input for next
• each stage complete before next is begun

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Waterfall Stages
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Waterfall Advantages

• Much better than chaos!
• Staged deliverables are possible
• Clearly defined stages help with
• planning, scheduling
• management, organization
• accountability, control

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Waterfall Disadvantages

• Not very practical (often do not know all
  requirements in the beginning)
• No feedback, provision for modification
• Customer sees nothing until last step

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Modified Waterfalls

• Sashimi (Overlapped Phases)
• start next stage before completing current stage
• Subprojects
• start parallel subprojects after architectural
  design
• Risk Reduction
• iterate during requirements

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SpiralModel
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Spiral Model

• Advantages
• more feedback from customer
• risk analysis -- spend more to reduce risk
• Disadvantages
• complicated

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Evolutionary Prototyping
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Evolutionary Prototyping

• Advantages
• useful when requirements are unknown or change
  rapidly
• allows for experimentation in architecture
• provides steady progress
• Disadvantages
• cannot predict schedule
• may be confused with code-and-fix

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Staged Delivery
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Staged Delivery

• Advantages
• customer gets early releases
• tangible signs of progress
• Disadvantages
• requires careful planning and management

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Design-to-Schedule
Ran out of time or money
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Design-to-Schedule

• Advantages
• similar to Staged Delivery
• guarantees release by a fixed date
• Disadvantages
• may waste planning effort on stages that are
  never completed

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Evolutionary Delivery
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Evolutionary Delivery

• Advantages
• lots of customer feedback
• Disadvantages
• hard to predict schedule

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Review of Incremental Models

• Spiral
• Evolutionary Prototyping
• Staged Delivery
• Design-to-Schedule
• Evolutionary Delivery

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SpiralModel
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Evolutionary Prototyping
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Staged Delivery
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Design-to-Schedule
Ran out of time or money
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Evolutionary Delivery
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Synchronize-and-Stabilize

• A version of incremental model used by Microsoft
• Interview customers
• Prioritize features to be added
• Divide work into several builds (parallel)
• Synchronize builds daily
• Stabilize after builds complete

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Rational Unified Process (RUP) Model
Process Workflow
Support Workflow