Waterfall Model

Waterfall model is also known as sequential development model. Waterfall model was proposed by Winston W. Royce during 1970s. This development model has been successfully used in several Organizations, U.S. Department of Defense and NASA. 

In Waterfall Model, one stage precedes other in a sequential manner and only after preceding stage is successfully completed. This model is simple and more disciplined software development approach. This model is effective only when each phase is completed successfully (100%) on time. 

Waterfall model also carries a reputation of not being a practical development model as it expects previous phase to be completed before moving on to next phase and does not accommodate any requirement changes during later phase of SDLC. This model can be successfully followed in small projects and when the requirements are clearly known and resources are available as planned. 

Waterfall model has the following stages:

1) Requirements specification
2) Design
3) Construction
4) Integration
5) Testing and defect fixing
6) Implementation
7) Maintenance

See the stages of Waterfall model represented Diagrammatically