Question

What is enhanced ER Model? Explain extended ER features: Specialization, Generalization and Aggregation with your clear definitions/ideas/differences in your own words and give at least one appropriate example for each one of them.

Answer 1

Enhanced ER Model (EER) :

• It is also known as Extended ER model.
• As the data is increasing, development of traditional ER model for database modeling is getting difficult. To reduce complexity of modeling we have EER model.
• It is a high-level data model also is an extension of original ER model, Enhanced ER diagrams are advance database diagrams which represents requirements and the complex database

.Features of EER Model :

• Creates designs more accurate to schema of database.
• It shows the constraints and data properties more precisely.
• it is an extension of Original ER model so it includes all modeling concepts of Original ER model.
• It is a diagrammatic Technique for showing Super Class and Sub Class i.e. leads to concept of Inheritance.
• It has concept of Specialization and Generalization, Union or Category, Aggregation.

Generalization

• It is a bottom-up approach. In this two or more low level entities combine to form a higher level entity, with attributes common to them.
• In Programming subclass are called specialized class and superclass are called generalized class, two or more sub class with some common properties combine to form a super class.
• Revere process of Specialization is Generalization.
• It is used to identify common features of the entities.
• Example : Teacher and Student entities can be combined and create a higher level entity Person.

Specialization :

• It is top-down approach. High level entities are broken down into multiple low level entities.
• It is opposite of Generalization.
• Each subclass of a superclass i.e. each subset of an entity have some distinguishing features.
• Specialization is usually done after Generalization, i.e. superclass is defined first after which sub classes can be defined.
• It identifies unique attributes of the members of an entity.

Example : In Employee management system, EMPLOYEE entity could be specialized as WRITER or TESTER based on roles they have in the company.

Aggregation :

• Aggregation is a process to depict the relationship between various entities, aggregated into high level entity.
• It is like data abstraction, as It abstracts relationship between multiple objects to a single object.
• In this process we consider two activities as single entities.

Example : STUDENT entity has a relation of works on with PROJECT entity and they together form a single entity that has a relationship "guides" with the entity MENTOR

HOPE THIS HELPS THUMBS UP :)