6.4 MODEL DYNAMICS
It has previously been implied that a type is essential a rule on the interpretation of a value. In the visual model, I proposed that the type of each contained object be made explicit. This gives a depth to the display by not indicating a named "black box", but rather providing some indication of the method of access. This object is visually defined by its type which in turn reveals certain rules of behavior that are employed in obtaining that object's value. This is in line with the contention of Wegner that categories be considered as a capacity to act rather than some thing [Wegner 91].
One would declare within a model, here is the named object and its type - or in different language, here is the object and the rules for obtaining the value within. In the onedim prototype modeling system, object type needed to be specified explicitly so that the opening behavior could be obtained. It should be noted that the model from which the object/model was opened probably does not influence behavior, the model that object was contained in was never a required piece of information.
Using a model as a type means using the model as a rule. Some interpretation may have to be made of that model to present it to the system for processing as a rule, but for all intents and purposes, it is a rule.
Other rules as well should be made explicit if they are contained in that model. In fact, rules should be contained in that model if they are as valuable in determining behavior of that model as that model's type is.