A modeling system for universal specification of user interfaces. The system provides a means for defining user interfaces, including highly complex and dynamic user interfaces, in a manner that is independent of any implementation context. The modeling system leads from a user-friendly visual representation of the user interface, through progressively detailed specifications of structural and behavioral aspects of the user interface parts, until a rigorous definition of the user interface in all its contexts of use is achieved. Using the information captured in the model, tools that automatically generate the fully working user interface code can be built.