Use Cases Part II: Taming Scope
http://www.alistapart.com/articles/tamingscope/

Carr, Norm and Tim Meehan
List Apart, A
2005

Abstract:

The use-case model can be a powerful tool for controlling scope throughout a project's life cycle. Because a simplified use-case model can be understood by all project participants, it can also serve as a framework for ongoing collaboration and a visual map of all agreed-upon functionality. Use it to plan, to negotiate, and to prevent scope creep.