The spiral model is a risk-driven approach to software development. Its repeated cycles are organized around reducing important uncertainties, rather than repeating a fixed set of coding tasks.
One Cycle
1.
Define the objective, alternatives, and constraints.
2.
Identify and evaluate the risks.
3.
Develop and check the next product or prototype.
4.
Review the outcome and plan the next cycle.
Example
If a service depends on an unfamiliar external system, a small integration prototype can answer whether the interface and response time are workable before the team commits to a large implementation. A different project may need a usability experiment or a capacity test instead.
Trade-offs
The model gives risk analysis an explicit place in planning, but identifying and evaluating risks requires judgment. More cycles and documents do not automatically reduce risk. Each cycle should leave evidence that supports the next investment or a decision to change direction.
