

The paper that started Waterfall - Bluem00
http://www.cs.umd.edu/class/spring2003/cmsc838p/Process/waterfall.pdf

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Bluem00
The first diagram in the paper is the commonly implemented version of
waterfall. Dr. Royce didn't intend for it to become so, however: "I believe in
this concept, but the implementation described above is risky and invites
failure."

He goes on to explain what else is required to do it correctly.

