Enhanced entity–relationship model


The enhanced entity–relationship model in computer science is a high-level or conceptual data model incorporating extensions to the original entity–relationship model, used in the design of databases.
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, telecommunications, complex software systems and geographic information systems.

Mechanics

The EER model includes all of the concepts introduced by the ER model. Additionally it includes the concepts of a subclass and superclass, along with the concepts of specialization and generalization. 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 types. EER model also includes EER diagrams that are conceptual models that accurately represent the requirements of complex databases.

Subclass and superclass

Entity type Y is a subtype of an entity type X if and only if every Y is necessarily an X. A subclass entity inherits all attributes and relationships of its superclass entity. This property is called the attribute and relationship inheritance. A subclass entity may have its own specific attributes and relationships. A common superclass example is a Vehicle superclass along with the subclasses of Car and Truck. There are a number of common attributes between a car and a truck, which would be part of the superclass, while the attributes specific to a car or a truck would make up two subclass

Tools