It was developed to reflect more precisely the properties and constraints that are found in more complex databases, such as in engineering design and manufacturing (CAD/CAM), telecommunications, complex software systems and geographic information systems (GIS).
Furthermore, it introduces the concept of a union type or category, which represents a collection of objects that is the union of objects of different entity types.
The EER model also includes EER diagrams that are conceptual models that accurately represent the requirements of complex databases.
This property is called the attribute and relationship inheritance.
Textbooks discussing EER and implementation using purely relational databases: Booklet discussing EER and implementation using object-oriented and object–relational databases: Textbook discussing implementation in relational and object–relational databases: Shorter survey articles: