The Waterfall Model

The Waterfall model (non iterative model) is a sequential software development model in which development is seen as flowing steadily downwards (like a waterfall) through the phases of requirements analysis, design, implementation, testing (validation), integration, and maintenance. Progress flows from the top to the bottom, like a waterfall. Thus the waterfall model maintains that one should move to a phase only when its preceding phase is completed and perfected. Phases of development in the waterfall model are thus discrete, and there is no jumping back and forth or overlap between them.

It is also called as Classic Life Cycle Model (or) Linear Sequential Model.


The advantage of waterfall model is that it allows for departmentalization and managerial control. A schedule can be set with deadlines for each stage of development and a product can proceed through the development process. Other advantages include

1. Testing is inherent to every phase of the waterfall model
2. It is an enforced disciplined approach
3. It is documentation driven, that is, documentation is produced at every stage

The disadvantage of waterfall model is that it does not allow for much reflection or revision (inflexible).

However, many projects rarely follow its sequential flow. This is due to the inherent problems associated with its rigid format. Namely:

1. It only incorporates iteration indirectly, thus changes may cause considerable confusion as the project progresses.
2. As the client usually only has a vague idea of exactly what is required from the software product, this model has the difficulty accommodating the natural uncertainty that exists at the beginning of the project.
3. The customer only sees a working version of the product after it has been coded & this may result in disaster if any undetected problems are precipitated to this stage.