UML and user interface modeling

UML and traditional CASE tools still focus more on application internals and less on application usability aspects. A user interface (UI) is modeled in terms of its internal structure and objects comprising it, the same as the rest of the application. The adoption of use cases and interaction scenarios acknowledges the importance of recognizing user tasks when developing an application, but it is still used mainly as a starting point for designing software implementing usage scenarios rather than focusing on modeling user tasks to improve application usability. Explicit modeling of user interface domain knowledge can bring important benefits when utilized by a CASE tool: additional design assistance with exploring UI design alternatives, support for evaluating and critiquing UI designs, as well as increased reuse and easier maintenance. UML can provide a notation framework for integrating user interface modeling with mainstream software engineering OO modeling. The built-in extensibility mechanisms (stereotypes, tagged values and constraints) allow the introduction of new modeling constructs with specialized semantics for UI modeling while staying within UML. The paper identifies modeling constructs needed for UI modeling and proposes a direction for extending UML to better address UI design.