Generalization and Specialization

1. Generalization

Generalization is a bottom-up approach in which multiple lower-level entity sets are combined into a single higher-level entity set based on common features.

• Combines similar entities
• Reduces data redundancy
• Improves data consistency

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

2. Specialization

Specialization is a top-down approach where a higher-level entity is divided into multiple lower-level entity sets based on distinguishing characteristics.

• Creates sub-entities
• Adds specific attributes
• Improves clarity

           [ EMPLOYEE ]
                 |
        ---------------------
        |                   |
   [ TEACHER ]          [ CLERK ]
     Subject              Section

3. Inheritance

In specialization, sub-entities inherit attributes of the super-entity automatically.

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

• Avoids duplication
• Ensures consistency

4. Types of Specialization

4.1 Disjoint Specialization

An entity can belong to only one sub-entity.

[ EMPLOYEE ]
      |
   (Disjoint)
      |
  TEACHER  CLERK

4.2 Overlapping Specialization

An entity can belong to more than one sub-entity.

[ PERSON ]
      |
 (Overlapping)
      |
 STUDENT  EMPLOYEE

5. Constraints in Generalization and Specialization

• Disjoint Constraint – entity belongs to only one subclass
• Overlapping Constraint – entity belongs to multiple subclasses
• Total Specialization – every entity must be a member of a subclass
• Partial Specialization – some entities may not belong to any subclass

Total Specialization → Double line
Partial Specialization → Single line

6. Difference between Generalization and Specialization

Generalization              Specialization
-------------------------  -------------------------
Bottom-up approach         Top-down approach
Combines entities          Divides entity
Common attributes          Specific attributes

7. Advantages

• Represents hierarchy clearly
• Reduces data redundancy
• Improves database design
• Supports inheritance

Practice Questions

1. Define generalization.
2. Define specialization.
3. Explain inheritance with example.
4. What are disjoint and overlapping constraints?
5. Differentiate between generalization and specialization.

Practice Task