Waterfall Model

The waterfall model is a sequential approach to software development in which requirements, design, implementation, testing and deployment proceed as separate phases, each completed before the next begins. The model is almost always traced to computer scientist Winston Royce's 1970 paper Managing the Development of Large Software Systems, but Royce's own paper argued against what industry practice later attributed to it: he called the single-pass version a simpler method, stated plainly that in my experience the simpler method has never worked on large software development efforts, and recommended iterative feedback loops between adjacent phases with major phases run twice. Later writers and practitioners cited Royce's paper, and especially its early illustrative diagram, in support of the rigid single-pass process he had explicitly warned against, one of the more consequential misreadings in software-engineering history, recorded as a dissent below. Whoever first used the word waterfall itself, the term became the standard name for the rigid process by the 1980s, commonly contrasted with the later iterative methods named agile.