Spiral model (Boehm) each cycle produces something to be evaluated, but not necessarily a usable system. Moreover, The Spiral model has the risk of analysis which the waterfall model hasn't. Its management of risk is built into model. It is integration of technical development and risk management because finer grain process and also rational incorporation of prototype because all prototypes serve to reduce risk. Specially, spiral model be propitious to large project development, and it is an effective method. However, if use spiral model must need more experience evolution of risk and precessional knowledge.
Obviously, each model has its use. We can not deliver waterfall model is not useful although it has some weakness, because it had been used widely last 20 years because of it support structural software design and can control complexity of software. If we focus on the development and maintenance of a diverse range of software products, waterfall model will be not appropriate. …
