Extended ER (EER) Features

Extended ER (EER) features enhance the basic ER model by adding
advanced concepts like specialization, generalization, inheritance,
and aggregation to model complex real-world scenarios.

1. What is Extended ER Model?

The Extended ER (EER) Model is an extension of the ER model that includes additional constructs to represent more complex relationships and data constraints.

Supports inheritance
Represents hierarchy
Models real-world complexity

2. Generalization

Generalization is a bottom-up approach where multiple lower-level entities are combined into a higher-level entity based on common attributes.

Car        Bike
  \          /
   \        /
    [ VEHICLE ]
       |
   Reg_No, Color

Bottom-up approach
Reduces redundancy

3. Specialization

Specialization is a top-down approach where a higher-level entity is divided into specialized lower-level entities.

        [ EMPLOYEE ]
              |
      -------------------
      |                 |
 [ TEACHER ]       [ CLERK ]

Top-down approach
Improves clarity

4. Inheritance

Inheritance allows sub-entities to inherit attributes of the super-entity.

[ EMPLOYEE ]
   |-- Emp_ID
   |-- Name
        |
     [ MANAGER ]
        |
     Department

Avoids repetition
Ensures consistency

5. Aggregation

Aggregation is used when a relationship between entities needs to be treated as a higher-level entity.

[ STUDENT ] --- Enrolls --- [ COURSE ]
          \_______________________/
                    |
               [ RESULT ]

Represents relationship as entity
Used in complex designs

6. Difference between Generalization and Specialization

Generalization              Specialization
-------------------------  -------------------------
Bottom-up approach         Top-down approach
Combines entities          Divides entity
Reduces redundancy         Adds specific details

7. Advantages of Extended ER Model

Models complex data
Supports inheritance
Improves database clarity
Reduces redundancy

Practice Questions

What is Extended ER model?
Explain generalization with diagram.
Explain specialization with diagram.
What is aggregation?
Differentiate between generalization and specialization.

Practice Task

Draw EER diagrams for: ✔ Vehicle classification system ✔ Employee specialization system ✔ Student–Course–Result system

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