Extended or Enhanced ER model

Extended or Enhanced ER model

Extended ER is a high-level data model that incorporates the extensions to the original ER model. Enhanced ER models are high level models that represent the requirements and complexities of complex databases.

The extended Entity Relationship (ER) models are three types as given below −

• Aggregation


• Specialization


• Generalization

Specialization

The process of designing sub groupings within an entity set is called specialization. It is a top-down process. If an entity set is given with all the attributes in which the instances of the entity set are  differentiated according to the given attribute value, then that sub-classes or the sub-entity sets can be formed from the given attribute.

Generalization

It is the reverse process of specialization. It is a bottom-up approach.

It converts subclasses to superclasses. This process combines a number of entity sets that share the  same features into higher-level entity sets.

If the superclass and sub-class information is given for the given entity set then, ISA relationship type will be used to represent the connectivity between the subclass and superclass as shown below –

Aggregation

It is an abstraction in which relationship sets are treated as higher level entity sets and can participate in relationships. Aggregation allows us to indicate that a relationship set participates in another relationship set.

Aggregation is used to simplify the details of a given database where ternary relationships will be changed into binary relationships. Ternary relation is only one type of relationship which is working between three entities.