What Makes a Good User Interface Pattern Language?

A developer of user interfaces (UI) should be able to employ a user interface pattern language to design acceptable user interfaces. But, what makes a good pattern language? Three types of validation were identified as requiring consideration: the validity of the individual patterns, the internal validation of the pattern language and the external validation of the pattern language. This paper investigates internal validity. A set of six tests that a developer can use to test the internal validity of a pattern language has been identified.