When you define a subclass, you may specify that the subclass replaces its superclass entirely. To turn on the feature for an individual entity class the Replace_Superclass property in the Rational Software Architect Curam Properties tab must be set to 1 - yes using the supplied drop-down.
For example, settingReplace_Superclass to yes for a class, MySubclass, means that instances of the base class, MyBaseClass, will no longer be created. All requests for the base class (MyBaseClass) will now receive an instance of the subclass (MySubclass). This is handled by the factory mechanism and is transparent to the user.