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 −
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.
Specialization of a person allows us to distinguish a person according to whether they are employees or customers. Specialization of account creates two entity sets: savings account and current account.
In the E-R diagram specialization is represented by triangle components labeled ISA. The ISA relationship is referred as superclass- subclass relationship as shown below −
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 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 −
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.
Aggregation is shown in the image below −