ER Diagram (Entity-Relationship)

About

An ER Diagram represents data models and relationships between entities in a database. It is widely used in database design and schema planning.

Refer to the official documentation for more details - https://plantuml.com/er-diagram

Entity Relationship Diagram (ERD)

Key Elements

1. Entities

   • Represented as rectangles, denoting real-world objects (e.g., Customer, Order).

2. Attributes

   • Represented as ellipses connected to entities.

   • Primary Key (PK) – Unique identifier (underlined).

   • Foreign Key (FK) – Connects to another entity.

3. Relationships

   • Represented as diamonds between entities (e.g., Places Order).

   • 1:1, 1:M, M:N relationships specify cardinality.

4. Cardinality & Participation

   • (1,1), (0,N), (M,N) define relationship constraints.

1. Employee Management System

This represents database entities and relationships for an Employee Management System.

• Entities (entity Name { }).

• Primary Keys (* field : type).

• Relationships (}|..||).

@startuml
title Employee Management - ER Diagram

entity Employee {
    * emp_id : INT
    --
    name : STRING
    age : INT
    department_id : INT
}

entity Department {
    * dept_id : INT
    --
    dept_name : STRING
}

Employee }|..|| Department : belongs_to

@enduml

2. Order System

This represents tables and their foreign key constraints.

@startuml
title Database Schema - Order System

entity Customers {
    * id : INT
    --
    name : STRING
    email : STRING
}

entity Orders {
    * id : INT
    --
    customer_id : INT
    total_amount : DECIMAL
}

entity Order_Items {
    * id : INT
    --
    order_id : INT
    product_id : INT
    quantity : INT
}

Customers ||--|{ Orders : has
Orders ||--|{ Order_Items : contains

@enduml