Waterfall model

 
Definition: Waterfall model is an example of a Sequential model. In this model, the software development activity is divided into different phases and each phase consists of a series of tasks and has different objectives. In waterfall, development of one phase starts only when the previous phase is complete.
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Definition: The waterfall model is a classical model used in system development life cycle to create a system with a linear and sequential approach. It is termed as waterfall because the model develops systematically from one phase to another in a downward fashion.

Phases of waterfall project management

• Requirement gathering and documentation. In this stage, you should gather comprehensive information about what this project requires. 
• System design. Using the established requirements, your team designs the system. 
• Implementation. 
• Testing. 
• Delivery/deployment.
• Maintenance.

Advantages: 

1. Easy to use, simple and understandable, 

2. Easy to manage as each phase has specific outputs and review process, 

3. Clearly-defined stages, 

4. Works well for smaller projects where requirements are very clear, 

5. Process and output of each phase are clearly mentioned in the document.

Disadvantages: 

1. It doesn’t allow much reflection or revision. When the product is in testing phase, it is very difficult to go back and change something which is left during the requirement analysis phase.
2. Risk and uncertainty are high.
3. Not advisable for complex and object-oriented projects.
4. Changing requirements can’t be accommodated in any phase.
5. As testing is done at a later phase. So, there is a chance that challenges and risks at earlier phases are not identified.