Waterfall model
The waterfall model is a software development model first proposed in 1970 by W. W. Royce, in which development is seen as flowing steadily through the phases of requirements analysis, design, implementation, testing (validation), integration, and maintenance.
In the original article, Royce advocated using the model repeatedly, in an iterative way. However, most people do not know that and some have discredited for use as a Real World process. In practice, the process rarely proceeds in a purely linear fashion. Iterations, by going back to or adapting results of the precedent stage, are common.
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