Our choice of the basis was constrained by our requirements. This formal description can then be used to drive the user interface at run time, and it can also serve additional purposes. The primary strength of user interface models is in their descriptive power and in their high level of abstraction. The data flow constraints are the control element in the model, they specify the dependencies between inputs, variables and objects. The original model consisted of actions, attributes, and an object hierarchy.
Actions have parameters, pre and postconditions.
The pre and postconditions capture part of an application action s semantics. James D. Foley, Won Chul Kim, Srdjan Kovacevic, and Kevin Murray. Defining user interfaces at a high level of abstraction .