Waterfall Model

Waterfall Method It was introduced by Winston Royce in 1970. Waterfall method of software development is the oldest and most of the software engineers are familiar with it. Some people think SDLC and Waterfall are same. It used to be same long time back when the software development was new and systems were not complex. It involves sequence of steps or stages. Output of one stage is input to another stage. Some time there are hard boundaries between the two stages and sometimes the two stages may overlap. Some software development teams may add or delete steps. Some may change the name of the steps according to their requirements. As this is a very straight forward method, it facilitates the project management, scheduling and estimation.

Once one phase of the software development is complete, the development of next phase starts. You cannot come back.

There are very definite goals for each phase of the development.
The biggest drawback of waterfall model is that it does not allow much of revision. It is very difficult to go back and change something. Some times the requirements are not well figured out in initial stage of the project.

The waterfall method is not suitable when requirements are changing. The customer or stakeholder wants to monitor the progress all the time and this is not suitable as you are working on only one phase at a time. It needs lot of effort on planning. All the phases are frozen and there is no turn around.

Typical Waterfall Phases



System Concept
System Requirements
System Design
Programming
Code & Unit Test
Integration & Test
Deployment


Here a sample diagram for Waterfall Model for SDLC. These are generic phases. These different phases can change depending upon a project.





Waterfall Model of SDLC