Entity-Relationship (ER) Model
⏱ Estimated reading time: 1 min
The Entity–Relationship (ER) Model, proposed by Peter Chen, is a conceptual data model used to design and visualize a database. It represents real-world entities and the relationships between them.
Key Components of ER Model
1️⃣ Entity
An object that exists in the real world and has distinguishable characteristics.
Examples: Student, Employee, Product.
Entity Types
-
Strong Entity — has its own primary key
-
Weak Entity — depends on another entity
2️⃣ Attributes
Properties of an entity.
Types:
-
Simple (Name)
-
Composite (Full Address)
-
Derived (Age from DOB)
-
Multivalued (Phone numbers)
-
Key Attribute (RollNo)
3️⃣ Relationships
Associations between entities.
Types of Relationships
-
One-to-One (1:1)
-
One-to-Many (1:M)
-
Many-to-Many (M:N)
Example:
Student — Enrolls — Course
4️⃣ ER Diagram Symbols
| Concept | Symbol |
|---|---|
| Entity | Rectangle |
| Weak Entity | Double rectangle |
| Attribute | Oval |
| Key Attribute | Underlined oval |
| Relationship | Diamond |
| Multivalued Attribute | Double oval |
Example
Student — Enrolls — Course
-
Student (SID, Name, Age)
-
Course (CID, Title)
-
Relationship: Enrolls (Date)
Conclusion
The ER Model provides a clear and structured method for designing a database at the conceptual level. It helps convert real-world problems into a database blueprint, which is later transformed into relational tables.
Register Now
Share this Post
← Back to Tutorials