This process model look like a spiral with many loops. The number of loops in the spiral model is not fixed or limited, we can add as many as required. Each of the loop is a phase in spiral model(e.g., A loop can be feasibility study , another loop could be requirement analysis).
Each of these phases is divided into 4 quadrants: Determine objectives, Identify and resolve risks, Prototype evaluation and Develop next level of product.
-Source : Software Engineering – IIT Kharagpur [M02L04]
Phases of Spiral Model
The phases of spiral model are the quadrants. Each quadrant has specific goals in the spiral model, given in point form below.
(A) First Quadrant (Goal or Objective Settings)
- First quadrant, objective of phase is set.
- Then all the risk associated with the objective is identified.
(B) Second Quadrant ( Risk Assessment and Reduction)
- Risks are analyzed for each project.
- Appropriate steps to resolve those risk is taken.
- If risks are unclear a prototype is build to get clarity on the technical or functional issues.
(C) Third Quadrant (Development and Validation)
- After removing all risks, develop the product and validate the next level of the product.
(D) Fourth Quadrant (Review and Planning)
- Review results with customer and plan the next iteration.
- In this way a more complete version of software is built.
When to use the SPIRAL Process Model ?
- Risk analysis is built into the model.
- Software product that complex in nature or carry more risk, then this process model is suitable.
- Project with high risk can also use this model.
- This process model not good for ordinary software projects.