Patterns need to be described and formalized in ways that enable the reader to determine whether the particular solution presented is useful and applicable to his or her problem in a given context. However, many pattern descriptions tend to focus on the solution to a problem, and not so much on how the various (and often conflicting) forces involved are balanced. This chapter describes the user requirements notation (URN), and demonstrates how it can be used to formalize patterns in a way that enables rigorous trade-off analysis while maintaining the genericity of the solution description. URN combines a graphical goal language, which can be used to capture forces and reason about trade-offs, and a graphical scenario language, which can be used to describe behavioral solutions in an abstract manner. Although each language can be used in isolation in pattern descriptions (and have been in the literature), the focus of this chapter is on their combined use. It includes examples of formalizing Design patterns with URN together with a process for trade-off analysis.
Textual User Requirements Notation