Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and the Unified Process, Second Edition

2.7. The Sequential “Waterfall” Lifecycle

In contrast to the iterative lifecycle of the UP, an old alternative was the sequential, linear, or “waterfall” lifecycle [Royce70]. In common usage, it defined steps similar to the following:

1.	Clarify, record, and commit to a set of complete and frozen requirements.
2.	Design a system based on these requirements.
3.	Implement, based on the design.

A two year study reported in the MIT Sloan Management Review of successful software projects identified four common factors for success; iterative development, rather than a waterfall process, was first on the list [MacCormack01].^[5]

^[5] The others were: 2) at least daily incorporation of new code into a complete system build, and rapid feedback on design changes ...