Waterfall model

The waterfall model is a sequential (non-iterative) design process, used in software development processes, in which progress is seen as flowing steadily downwards (like a waterfall) through the phases of conception, initiation, analysis, design, construction, testing, production/implementation and maintenance.

The waterfall development model originates in the manufacturing and construction industries: highly structured physical environments in which after-the-fact changes are prohibitively costly, if not impossible. Because no formal software development methodologies existed at the time, this hardware-oriented model was simply adapted for software development.

The first known presentation describing use of similar phases in software engineering was held by Herbert D. Benington at Symposium on advanced programming methods for digital computers on 29 June 1956. This presentation was about the development of software for SAGE. In 1983 the paper was republished with a foreword by Benington pointing out that the process was not in fact performed in a strict top-down fashion, but depended on a prototype.

The first formal description of the waterfall model is often cited as a 1970 article by Winston W. Royce, although Royce did not use the term waterfall in that article. Royce presented this model as an example of a flawed, non-working model; which is how the term is generally used in writing about software development—to describe a critical view of a commonly used software development practice.

The earliest use of the term "waterfall" may have been in a 1976 paper by Bell and Thayer.

In 1985, the United States Department of Defense captured this approach in DOD-STD-2167A, their standards for working with software development contractors, which stated that "the contractor shall implement a software development cycle that includes the following six phases: Preliminary Design, Detailed Design, Coding and Unit Testing, Integration, and Testing".

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