Information Modeling and Relational Databases, 2nd Edition

6.6. Generalization of Object Types

The previous section discussed a specialization procedure in which subtypes of a more general object type are introduced to declare that specific roles are recorded only for these subtypes. Apart from this top-down procedure, a subtype graph may also arise in a bottom-up way when we need to introduce a supertype of object types that already occur in the model.

The process of introducing a supertype for object types that already exist is known as object type generalization. Hence generalization is the reverse of specialization. A supertype is a more general form of its subtypes, and a subtype is a special form of its supertype(s).

Step 3 of the CSDP outlined the main reasons for generalizing existing object ...