EER模型对ER模型进行了那些扩充？

The EER Model includes all of the modelling concepts introduced by the ER model. Additionally it includes the concepts of a subclass and superclass, along with the concepts of specialisation and generalisation. Furthermore, it introduces the concept of a union type or category, which is used to represent a collection of objects that is the union of objects of different entity types.

关键词:subclass and superclass; specialisation and generalisation; union type