What is ER Model?
The Entity Relationship (ER) Model is a conceptual data model used to represent the structure of a database. It describes data using entities, attributes, and relationships.
Entity
An Entity is a real-world object that can be identified uniquely. Examples include Student, Employee, Product, and Customer.
Attributes
Attributes describe the properties of an entity. For example, a Student entity may have Roll Number, Name, and Age.
- Simple Attribute
- Composite Attribute
- Single-Valued Attribute
- Multi-Valued Attribute
- Derived Attribute
Relationship
A Relationship represents an association between entities. For example, Student studies Course.
Types of Relationship
- One-to-One (1:1)
- One-to-Many (1:M)
- Many-to-One (M:1)
- Many-to-Many (M:N)
ER Diagram Symbols
- Rectangle → Entity
- Ellipse → Attribute
- Diamond → Relationship
- Double Ellipse → Multi-Valued Attribute
- Dashed Ellipse → Derived Attribute
Advantages of ER Model
- Easy to understand
- Provides clear database design
- Improves communication between users and developers
- Helps in database implementation