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.
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