37. In a computing environment, a method for specifying a hierarchy of user-defined classes of graphical objects comprising the steps of: identifying a first class of graphical objects; and identifying at least one descendant class of graphical objects that is a subclass of the first class of graphical objects for the hierarchy of classes of graphical objects; graphically depicting a relationship between the first class of graphical objects and the at least one descendent class of graphical objects; inheriting, with the at least one descendant class of graphical objects, aspects of the first class of graphical objects; graphically depicting contents of the at least one descendant class of graphical objects, wherein the contents include the aspects that are inherited from the first class of graphical objects; incorporating an instance of the first class of graphical objects in a graphical model; initiating execution of the graphical model; instantiating the first class of graphical objects; instantiating at least one of the at least one descendant classes of graphical objects; dynamically specifying one of the first class of graphical objects or the at least one descendant class of graphical objects that is instantiated after initiating execution.
50. The method of claim 37 , wherein the method further comprises inserting a graphical symbol that represents classes of a hierarchy of classes into a graphical model; and graphically specifying that the graphical symbol represents an instance of one of the first class of graphical objects or the at least one descendant class of graphical objects.