14. Spiral model

With the spiral model, the project is carried out as a series of complete loops that go through most of the system life cycle process (except maintenance of course).

Each loop produces a 'prototype' of some aspect of the system. The user gets a chance to assess the prototype to confirm that that bit of the system is working as required. Then the next loop develops another prototype to simulate another part of the system. Once again they can assess that aspect of the system.

The idea is to perfect a smaller chunk of the overall project before going forward with the rest of the system thus minimising risk of the project going astray.