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EER Model

Some applications like - GIS, CAD/CAM, Telecommunication Have more complex requirements than normal database applications. To meet the requirements additional modeling concepts were incorporated into Conceptual data modeling such as ER modeling. The result is EER, stands for Extended ER modeling or Enhanced ER modeling.
The additional EER concepts are used to model applications more completely and more accurately. EER includes some object-oriented concepts, such as inheritance.

Additional concepts:
  • Subclasses/super classes
  • Specialization/generalization
  • Attribute and relationship Inheritance
These are fundamental to conceptual modeling.

1. Subclasses/Super class of an Entity type
An entity type may have additional meaningful subgroupings of its entities. These are called superclass/subclass relationships
Note: An entity that is member of a subclass represents the same real-world entity as some member of the superclass:
  • The subclass member is the same entity in a distinct specific role
  • An entity cannot exist in the database merely by being a member of a subclass; it must also be a member of the superclass
  • A member of the superclass can be optionally included as a member of any number of its subclasses
2. Specialization/Generalization in EER
Specialization is the process of defining a set of subclasses of a superclass.

Generalization is the reverse of the specialization process. Several classes with common features are generalized into a superclass. Original classes become its subclasses

Generalization in EER

Double line indicates total participation with subclass entity.

Generalization in EER

Single line indicates partial participation with subclass entity. That means superclass may not be belogs to sub class entity always. Employee can be Manager, which is not avail in the diagram. and also for employee total particapation with salary as employee is eigther engineer or manager they will be salaried.

total participation with subclass in EER