ER Diagrams (Entity-Relationship Diagrams)

An ER Diagram (Entity-Relationship Diagram) is a graphical representation of the structure of a database. It is used to visually model entities, attributes, and relationships between data in a system. ER diagrams help in designing the database before implementation.

ER diagrams are mainly used during the database design phase to clearly understand how different data elements are connected.

🔹 Main Components of ER Diagrams

1️⃣ Entity

An Entity represents a real-world object or concept.
Examples: Student, Employee, Course

Symbol: Rectangle

2️⃣ Attribute

An Attribute describes the properties of an entity.
Examples: Student_ID, Name, Age

Symbol: Oval

Types of attributes:

  • Simple attribute

  • Composite attribute

  • Multivalued attribute

  • Derived attribute

3️⃣ Relationship

A Relationship shows how two or more entities are connected.
Example: A Student enrolls in a Course

Symbol: Diamond

🔹 Types of Relationships

  • One-to-One (1:1)

  • One-to-Many (1:N)

  • Many-to-Many (M:N)

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