Answer
The Waterfall Model was the first Process Model to be introduced. It is also referred to as a linear-sequential life cycle model. It is very easy to understand and use. In a waterfall model, each phase must be completed fully before the next phase can begin. This type of software development model is basically used for the project which is small and there are no uncertain requirements.
At the end of each phase, a review takes place to determine if the project is on the right path and whether or not to continue or discard the project.
Work Step by Step
The Waterfall Model was the first Process Model to be introduced. It is also referred to as a linear-sequential life cycle model. It is very easy to understand and use. In a waterfall model, each phase must be completed fully before the next phase can begin. This type of software development model is basically used for the project which is small and there are no uncertain requirements.
At the end of each phase, a review takes place to determine if the project is on the right path and whether or not to continue or discard the project.
In this model, software testing starts only after the development is complete. In the waterfall model phases do not overlap.
see the following picture:
