In the waterfall model, it is very important to take thesign-offof the deliverables of each phase. As of today most of the projects are moving withAgileand Prototype models, The Waterfall model still holds good for smaller projects. If requirements are straightforward and testable, the Waterfall model will yield the best results.
The spiral model is a combination of sequential and prototype models. This model is best used for large projects which involve continuous enhancements. There are specific activities that are done in one iteration (spiral) where the output is a small prototype of the large software. The same acti...