ER Diagrams and EER Concepts in DBMS

Detailed explanation with examples for Specialization, Generalization, and Aggregation.

1. ER Diagram Basics

An ER Diagram visually represents entities, attributes, and relationships in a database.

Example: [Student] —enrolls in— [Course]

Enhanced ER (EER) Diagrams include advanced modeling concepts:

Define subclasses from a superclass; subclasses inherit attributes from superclass.

Example:

Superclass: Employee(emp_id, name, salary)
Subclasses: Teacher(subject, department), Staff(role, work_shift)

Diagrammatically:

       Employee
      /       \
   Teacher     Staff

Combine multiple subclasses into a superclass.

Example:

Subclasses: Car(num_doors), Truck(load_capacity)
Superclass: Vehicle(vehicle_id, make, model)

Diagrammatically:

   Car    Truck
      \   /
      Vehicle

Treat a relationship as a higher-level entity.

Example: Project assigned to Department via Works_On; monitored by Manager.

[Department] — Works_On — [Project]
      \                     /
       \—— Monitors — [Manager]

Here, Works_On becomes an aggregate entity.

Concept	Definition	Example
Specialization	Create subclasses from superclass	Employee → Teacher, Staff
Generalization	Combine subclasses into superclass	Car, Truck → Vehicle
Aggregation	Treat relationship as an entity	Works_On relationship as aggregate