Extended ER Features

Extended ER Features

Extended ER Features

  • Specialization
  • Generalization
  • Attribute Inheritance
  • Aggregation
Specialization
The process of designating sub groupings with in an entity set is called specialization.We use IS A relationship to represent specialization.IS A relationship may also be referred as super class-subclass relationship
Example: Person IS A   Employee
               Person IS A   Customer
 
             Employee IS A Manager
 
Generalization
Here the design process take place in bottom up manner.Multiple entity sets are synthesized into a higher level entity set on the basis of common features.
Example: Employee and Customer entities can be synthesized into a higher level entity Person.
 
Attribute inheritance
The attributes of higher level entity set are inherited by lower level entity set.
 
Aggregation
Aggregation is an abstraction in which relationship sets are treated as higher level entity sets. Here a relationship set is embedded inside an entity set, and these entity sets can participate in relationships.