Extended Entity Relationship Model (EER Diagram)
September 17, 2016
Categorised in: Database Management System
The E-R model that is supported with the additional semantic concepts is called the extended entity relationship model.
- Specialization: It is the process of designation subgroupings within an entity set. It is a Top-down process. Example: Person – <IS A> – Employee – Customer
- Generalization: It is the process of defining a more general entity type from a set of more specialized entity types. Example: Person
Condition defined constraint: In condition-defined lower-level entity sets, membership is evaluated on the basis of whether or not an entity satisfies an explicit condition or predicate. Example: Account_type = “checking account”
User defined constraint: These types of constraints are defined by user. Example: After 3 months of employement bank assigns the employee to a team.
Disjoint: A disjointness constraint requires that an entity belong to only one lower-level entity set.
Overlapping: In overlapping generalization, the same entity may belong to more than one lower-level entity set within a single generalization.
Total generalization or specialization
Partial generalization or specialization
- Aggregation:It is an abstraction through which relationships are treated as higher-level entities.