<programming> A software life-cycle or product life-cycle model, described by W. W. Royce in 1970, in which development is supposed to proceed through the phases of requirements analysis, design, implementation, testing (validation), integration and maintenance. The waterfall model is also known as ADDIE, for analysis, design, development, implementation, evaluation. The expectation is that each earlier ("upstream") phase will be completed, and signed-off, before the following ("downstream") phase is started, often each by a different team. The name suggests a uni-directional flow of deliverables from one phase to the next in which "going back to the drawing board" is a major disruption.
Waterfall is ill-suited to projects requiring rapid prototyping and an exploratory approach to development. It is considered old-fashioned or simplistic by proponents of agile development which often uses the spiral model or iterative model instead. These more flexible approaches emphasise early and frequent delivery of useable, if incompete, products in order to gather constant feedback from users or other customers. This feedback guides the evolution of the design so it can adapt to changing requirements as understanding of the product improves.
[W. W. Royce, "Managing the Development of Large Software Systems", Proceedings of IEEE WESCON, August 1970].
Last updated: 2014-02-24
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