Friday, December 28, 2012

Spiral Model

Adds risk analysis, and 4gl RAD prototyping to the waterfall model.
Each cycle involves the same sequence of steps as the waterfall process model.

Spiral Model
Typical Activities:
  • Create a design
  • Review design
  • Develop code
  • Inspect code
  • Test product

Spiral Model Strengths:
  • Provides early indication of insurmountable risks, without much cost.
  • Users see the system early because of rapid prototyping tools.
  • Critical high-risk functions are developed first.
  • The design does not have to be perfect.
  • Users can be closely tied to all life-cycle steps.
  • Early and frequent feedback from users.
  • Cumulative costs assessed frequently.

Spiral Model Drawbacks:
  • Time spent for evaluating risks too large for small or low-risk projects.
  • Time spent planning, resetting objectives, doing risk analysis and prototyping may  be excessive.
  • The model is complex.
  • Risk assessment expertise is required.
  • Spiral may continue indefinitely.
  • Developers must be reassigned during non-development phase activities.
  • May be hard to define objective, verifiable milestones that indicate readiness to proceed through the next iteration.

When to use Spiral Model:
  • When creation of a prototype is appropriate.
  • When costs and risk evaluation is important.
  • For medium to high-risk projects.
  • Long-term project commitment unwise because of potential changes to economic priorities.
  • Users are unsure of their needs.
  • Requirements are complex.
  • New product line.
  • Significant changes are expected.

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