Spiral Model

The spiral model gives more emphases placed on risk analysis. The spiral model has four phases: Planning, Risk Analysis, Engineering and Evaluation. A software project repeatedly passes through these phases in iterations (called Spirals in this model). The baseline spiral, starting in the planning phase, requirements are gathered and risk is assessed. Each subsequent spirals builds on the baseline spiral.

Requirements are gathered during the planning phase. In the risk analysis phase, a process is undertaken to identify risk and alternate solutions. A prototype is produced at the end of the risk analysis phase.

Software is produced in the engineering phase, along with testing at the end of the phase. The evaluation phase allows the customer to evaluate the output of the project to date before the project continues to the next spiral.

In the spiral model, the angular component represents progress, and the radius of the spiral represents cost.

Advantages

a. High amount of risk analysis.

b. Good for large and mission-critical projects.

c. Software is produced early in the software life cycle.

Disadvantages

a. Can be a costly model to use.

b. Risk analysis requires highly specific expertise.

c. Project’s success is highly dependent on the risk analysis phase.

           d. Doesn’t work well for smaller projects.