The Waterfall

Life Cycle methodology is sometimes called the Waterfall method. In this classic view of system development the cycle is seen as a journey down a river with the end of each phase being a waterfall. The project moves forward in a linear fashion just as you would paddle down the stream. A preceding phase must be completed before the next starts. And, once you go over a waterfall (i.e., complete a phase) you can't go back.

Kendall and Kendall do not use the waterfall analogy in describing SDLC. Further, their description of SDLC allows for some degree of overlapping or concurrence in SDLC activities rather than being rigidly linear.

Kendall and Kendall say, "Although each phase is presented discretely [in the text book], it is never accomplished as a separate step. Instead, several activities can occur simultaneously, and activities may be repeated. It is more useful to think of the SDLC as accomplished in phases (with activities in full swing overlapping with others and then tapering off) and not in separate steps." (page 10, 5th edition)