The SPIRAL model is similar to the incremental model, but incorporates 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 spiral builds on the baseline spiral. Requirements are gathered during the planning phase.

This model of development combines the features of the prototyping model and the WATERFALL model. The spiral model is intended for large, expensive, and complicated projects.

The spiral model is similar to the incremental model, but incorporates 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 spiral builds on the baseline spiral. Requirements are gathered during the planning phase.

This model of development combines the features of the prototyping model and the waterfall model. The spiral model is intended for large, expensive, and complicated projects.