A Toolkit of Mechanism and Context Independent Widgets

ion, Control) [3] are both agent based models, where an agent is defined to have "state, possess an expertise, and is capable of initiating and reacting to events." [4]. An interface is built using hierarchies of agents. These agents represent an object in the application. In MVC, the model describes the semantics of the object, the view provides the (normally visual) representation of the object and the controller handles user input. In PAC, the abstraction describes the functional semantics of the object, the presentation handles the users interaction with the object, both input and output and the control handles communication between the presentation and the abstraction as well as between different PAC agents. The toolkit is object-oriented like both MVC and PAC, with each widget (or agent) encapsulated into different objects. Our toolkit, however, does not define the whole user interface in terms of a hierarchy of agents, but rather defines the individual widgets without specifying..