Extended / Enhanced ER (EER) Diagram

 

Extended / Enhanced ER (EER) Diagram

 

•       EER diagram stands for Enhanced (or Extended) Entity Relationship Diagram.

•       EER is a high-level data model that incorporates the extensions to the original ER model.

•       Enhanced or Extended ER Diagrams are high level models that represent the requirements and complexities of complex database.

•       In addition to ER model concepts EER includes Specialization, Generalization and Aggregation.

 

Generalization & Specialization

 

Generalization: 

    Generalization is a process of generalizing an entity which contains generalized attributes or properties of generalized entities. It is a Bottom up process i.e. consider we have 3 sub entities Car, Truck and Motorcycle. Now these three entities can be generalized into one super class named as Vehicle.

Specialization: 

   Specialization is a process of identifying subsets of an entity that share some different characteristic. It is a top down approach in which one entity is broken down into low level entity.

Another approaches to depict EER diagrams

Example 1

Here, d means disjoint

Example 2: 

Here, O means Omni or all.

Aggregation

In aggregation, the relation between two entities is treated as a single entity. In aggregation, relationship with its corresponding entities is aggregated into a higher level entity.

 Example: 

 

Center entity offers the Course entity act as a single entity in the relationship which is in a relationship with another entity visitor. In the real world, if a visitor visits a coaching center then he will never enquiry about the Course only or just about the Center instead he will ask the enquiry about both.

 Converting E-R Diagrams into Table

Below is the ER diagram:

This is conversion of the above ER diagram into tables:

 

Notable points:

1. As Age is derived attribute, so it will not be mentioned in the table conversion.

2. As Hobby is multivalued attribute, it is converted into separate table associate with the STUDENT table.

 Converting EER Diagrams into Table

Below is the EER diagram:

Tables will be:

1. CUSTOMER (pname, mobileno, address, cust_type)

2. FULLTIME (pname, mobileno, address, dept, desig)

3. PARTTIME (pname, mobileno, address, dept, #days, job)

4. ADHOC (pname, mobileno, address, dept, hours)

 Notable points:

1. The entities which are further classified into sub - entities; will not be converted into table. 

2. However their attributes will be a part of their sub-entities.