RUT - development handbook 1.3 The Spiral Model v 4.0
Fredrik Herbertsson · 2007
The idea behind the spiral model is to do system development incrementally while using another development model, such as the waterfall model for each development step. This can help mitigate the risks by not requiring the entire system to be defined at the start of the development. Instead, the most important parts are defined and implemented first. Using the experience gained from this you then go back to define and implement other parts of the system and so on.