ER Diagram Basics

You’ve identified your café data customers, orders, and items.
You understand their details and relationships.

Now imagine explaining all this to your team… just using words
Confusing, right?

So instead, you draw a simple diagram: boxes, lines, and shapes.
Suddenly, everything becomes clear.

That visual representation is called an ER Diagram.

An ER Diagram (Entity-Relationship Diagram) is a visual representation of:

• Entities
• Attributes
• Relationships

It helps you see the database structure before creating it

Symbols Used in ER Diagram

Each component has a specific symbol:

Supporting Explanation

Quick trick to remember:

• ???? Rectangle = “Thing”
• ⚪ Oval = “Details”
• ???? Diamond = “Connection”

Types of Attributes in ER Diagram

Attributes are not all the same. They have types:

Technical Example

Key Rules While Drawing ER Diagram

✔ Use clear names for entities
✔ Avoid duplicate attributes
✔ Define relationships properly
✔ Show primary keys (important attributes)

Real Life Example

1. College System
   • Student → Enrolls → Course
2. Bank System
   • Customer → Owns → Account
3. E-commerce
   • User → Places → Order