Concept of Generalization
Generalization is a process in the Entity-Relationship (E-R) model where common
characteristics from two or more entities are combined into a single, higher-level entity. It is
an abstraction mechanism that emphasizes the similarities among entities by grouping them
into a generalized (parent) entity.
Key Features of Generalization
1. Abstraction: Focuses on common features and ignores differences among entities.
2. Parent Entity: The generalized entity at a higher level.
3. Child Entities: The specific entities that are combined into the parent entity.
Representation in E-R Diagram
• Generalization is typically represented using a triangle pointing upward from the child
entities to the parent entity.
Example of Generalization
Scenario
In a database for a university:
• Entities: Student, Professor, Admin_Staff
• Common attributes for these entities: Name, Address, Contact
Generalization Process
• Combine Student, Professor, and Admin_Staff into a generalized entity Person.
• The Person entity will contain the common attributes (Name, Address, Contact).
• The specific attributes (Roll_No for Student, Emp_ID for Professor and Admin_Staff)
remain in their respective child entities.
E-R Diagram Representation
[Person]
▲
|
------------------------|
|
|
Student Professor Admin_Staff
• Person: Generalized entity with attributes Name, Address, Contact.
• Student: Specialized entity with an additional attribute Roll_No.
• Professor: Specialized entity with an additional attribute Emp_ID.
• Admin_Staff: Specialized entity with an additional attribute Dept.
Key Characteristics
1. Top-Down Approach: Generalization is typically viewed as a top-down design
process.
2. Commonality: The focus is on identifying shared attributes or behaviors.
3. Simplification: Helps reduce redundancy by grouping similar entities.
4. Hierarchy: Establishes a hierarchy of entities, with the generalized entity at the top.
Advantages of Generalization
1. Data Simplification: Reduces redundancy by centralizing shared data.
2. Efficient Design: Provides a cleaner and more organized database structure.
3. Reusability: Common attributes can be reused by multiple specialized entities.
4. Ease of Maintenance: Changes to common attributes need to be made only in the
generalized entity.
Real-World Examples
1. Transportation System:
• Generalized Entity: Vehicle
• Child Entities: Car, Bike, Truck
• Common Attributes: Registration_No, Owner
• Specialized Attributes: Car_Type (for Car), Payload (for Truck)
2. E-Commerce:
• Generalized Entity: Product
• Child Entities: Electronics, Clothing, Books
• Common Attributes: Product_ID, Price
• Specialized Attributes: Warranty (for Electronics), Author (for Books)