You can specify that one class is a subclass of another by creating an Isa relationship. This can be done with the associated Insert menu item, or several context menu items. The options in the Insert menu and the schema context menu prompt for two objects (classes or associations), the first one is the subclass, the second one being the super-class. Classes can only be a subclass of classes, and associations can only be a subclass of a associations. In the class and association context menu, there are also another two items for creating new Isa relationship. You can create ta new Isa with the current class/association playing the parent role, or the child role. In each case ICOM will prompt for another class/association for the correspondent role in the Isa relationship.
You can add additional descendent objects to a subsumption relationship with the compose isa menu item also available from the class and association context menu. In this case, the currently selected class/association will be the new child in a previously existing Isa relationship.
By default, an Isa node only specifies that a set of objects is the subclasses of another object, but nothing more. Similar to roles, Isa node can be further customised using checkboxes in the respective Data tab panel. Totality expresses that the super-class object is a union of all subclasses (covering). While exclusiveness expresses that all subclasses may be disjoint (mutually exclusive) from each other. There is a different graphical representation for regular, total, exclusive and total-exclusive isa relationships defined in this way.
IsA relationships can be removed in the same way as classes and associations, with the function.
Pablo Fillottrani 2010-08-17