Waterfall
The waterfall model derives its name due to the cascading effect from one phase to the other. In this model each phase has a well-defined starting and ending point, with identifiable deliveries to the next phase. Note that the arrow goes up and down the “waterfall”, reflecting the fact that developers often have to re-work earlier stages in the light of experience gained as development signs of progress.
Rapid Application Development
The spiral model follows an ‘incremental’ approach. Once a prototype is built it is evaluated on various parameters like strengths and weaknesses, risk, etc. Follows the discipline of the waterfall model and each SDLC step is followed for all prototypes built: Requirements gathering, Systems Design, Implementation, Testing and finally Evaluation feeds back into new requirements.
Spiral Model
The Spiral Model actually has aspects from other models such as
the waterfall, incremental and RAD. The difference with the spiral model is that it is risk-driven. It acknowledged that risk is that the heart of many large-scale development projects. It is designed to take into account these risks while they arise in the project and then deal with them before they become major problems. The model has 4 stages, each taking up one quadrant of the spiral. Objectives and requirements are determined in quadrant one, followed by risks and issues. A prototype is then developed which is tested in quadrant three. After this, the project is either completes or if the user wants more the final quadrant works on what will go into the next spiral.
Computer Science 