Spiral Model: refine through repeated rounds
The spiral model combines the waterfall model and the prototyping model. We incrementally build the software, get feedback and refine.
| In each iteration | What the team does |
|---|---|
| 1 | Determine objectives, alternatives and constraints for this iteration |
| 2 | Evaluate alternatives, identify and resolve risks |
| 3 | Develop and test, and release the product to the client |
| 4 | Plan the next phase |
At each iteration the prototype is refined compared to the previous version.
Unlike the waterfall model, where everything is documented at the beginning, requirement documents are developed across iterations as and when they are needed, and the software eventually evolves into the final product. Customers are involved at the end of every iteration, which reduces misunderstandings between the client and the developers. Drawback: iterations still take a long time — around 6 to 24 months each.
REMEMBER Spiral = planned iterations + explicit risk evaluation + customer feedback.
Models in the Plan and Document perspective: Waterfall, Prototype, Spiral