Waterfall model

The Waterfall Model was first Process Model to be introduced. It is also referred to as a linear-sequential life cycle model. It is very simple to understand and use. In a waterfall model, each phase must be completed fully before the next phase can begin. 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 waterfall model phases do not overlap.

Diagram of Waterfall-model: 

              

Advantages of waterfall model: 

• Simple and easy to understand and use. 
• Easy to manage due to the rigidity of the model – each phase has specific deliverables and a review process. 
• Phases are processed and completed one at a time. 
• Works well for smaller projects where requirements are very well understood. 

Disadvantages of waterfall model: 

• Once an application is in the testing stage, it is very difficult to go back and change something that was not well-thought out in the concept stage. 
• No working software is produced until late during the life cycle. 
• High amounts of risk and uncertainty. 
• Not a good model for complex and object-oriented projects. 
• Poor model for long and ongoing projects. 
• Not suitable for the projects where requirements are at a moderate to high risk of changing. 

When to use the waterfall model: 

• Requirements are very well known, clear and fixed. 
• Product definition is stable. 
• Technology is understood. 
• There are no ambiguous requirements 
• Ample resources with required expertise are available freely 
• The project is short.