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.

IMPORTANT LINKS:

Topic: SDLC Models.

Previous: Incremental Model.

Next: |   Agile SDLC  |   Waterfall Model   |   Iterative Waterfall Model    |   V-Model   |   RAD Model   |

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