Which of the following is not included in the waterfall model?

Explanation

The classical waterfall model consists of the sequential phases requirement analysis and specification, design, coding and unit testing, integration and system testing, and maintenance. There is no separate risk-handling activity anywhere in that sequence — this is the model's best-known weakness, since problems are discovered only late, when a phase's output is finally tested. Explicit risk analysis is the defining feature of Boehm's spiral model, where every loop begins with identifying and resolving risks. Requirement analysis, design and coding are all genuine waterfall phases, so the one not included is risk analysis.