The spiral model combines the waterfall model and the rapid prototyping model. The biggest advantage is that it emphasizes risk analysis and helps to integrate software quality into development; building large software in small segments makes it easy to calculate costs; customer participation ensures project controllability. But the build process is too cumbersome for large projects and not for small ones.
The figure above shows the 4 quadrants of the spiral model: planning, risk analysis, project implementation, and customer evaluation. The meanings of each quadrant are as follows.
(l) Formulate a plan: determine the software goal, formulate an implementation plan, and list the constraints of project development.
(2) Risk analysis: Evaluate the formulated implementation plan, identify risks and eliminate them.
(3) Implementation engineering: develop products and verify them.
(4) Customer evaluation: The customer reviews and evaluates the product, puts forward suggestions for correction, and formulates plans for the next step.
In the spiral model, each iteration needs to go through these 4 steps until the final product is perfect and can be submitted.
The spiral model is a strong form of risk analysis, which means that both alternatives and constraints are evaluated, and it is more helpful to incorporate software quality as a special goal into product development. It builds large-scale software in small segments, making cost calculation simple and easy, and customers always participate in the development of each stage, ensuring that the project does not deviate from the correct direction and also ensures the controllability of the project.