At one of software development methodology, most basic and general development model. The development model where it divides the whole project into several processes, defines result ones (document of specification and project book etc.) with each process clearly, on the basis of that result ones job of post-treatment consecutively keeps doing.

With waterfall model, development process software development life cycle (SDLC: Software development lifecycle) and the like paralleling, it divides into the shape such as "request" "specification" "analysis" "design" "programming" "inspection" "use". For example and it keeps promoting project with the procedure that it draws up the project book with design process, it programs on the basis of that project book. Any result things are verified in each every process, just those which are approved with specified procedure advance to the following process. Because the fact that it jumps over this order principlly, goes backward is not permitted, comparing to the circumstances where the water of the cascade runs down, it is called the waterfall model.

You can call original waterfall model development, development process of the document drive type which designates that the principle, "definition by the specification" is applied strictly as purpose. It can foresee the whole, from the point such that it can make schedule plan and resource allocation and the management of progress easy, even presently with large-scale project this method is taken basically.

That it has become prototype of the waterfall model it assumes that it is dissertation of wince ton W Royce (Winston W.Royce) who, is announced in 1970. In this dissertation it documents, both importance of the review, downstream process goes extra andreturns tohigh-level process the "feedback loop" was lectured. In addition either the language, "waterfall" is not used. According to other version, feedback missed the occasion where it is adopted to the troop standard of the Department of Defense, it assumes that this spread to the world.

Because as for the waterfall model which understands generally they are the sequential development types which do not permit the hand return, the ? ? trap to be in actual condition of the work, actual software development where feedback between process occurs inevitably criticism it is many. In addition, the waterfall from the fact that enormous time is required for project management and the fact that etc. system development needs to appointment for payment date are strong shortly, has been lectured also the model and the like which is compromised with repetitive opening departure technique and the like.