Coronel, Carlos Morris, Steven Rob, Peter (2011).
Fundamentals of Database Systems (6th ed.). Textbooks discussing EER and implementation using purely relational databases: Fundamentals of database systems (Seventh ed.). ^ "Enhanced Entity–Relationship Model".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 (such as max payload, truck type.) would make up two subclasses.
A common superclass example is a Vehicle superclass along with the subclasses of Car and Truck. A subclass entity may have its own specific attributes and relationships (together with all the attributes and relationships it inherits from the superclass). This property is called the attribute and relationship inheritance. A subclass entity inherits all attributes and relationships of its superclass entity. EER model also includes EER diagrams that are conceptual models that accurately represent the requirements of complex databases.Įntity type Y is a subtype (subclass) of an entity type X if and only if every Y is necessarily an X. 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. Additionally it includes the concepts of a subclass and superclass ( Is-a), along with the concepts of specialization and generalization. The EER model includes all of the concepts introduced by the ER model. See also: Entity–relationship model and Unified Modeling Language
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