History of ER models

ER diagrams are visual tools that are helpful to represent the ER model. Peter Chen proposed ER Diagram in 1971 to create a uniform convention that can be used for relational databases and networks.

What is a Relational Database:

A relational database means a database in which tables have some relation among themselves.

These relations are developed with the help of keys (primary, foreign, candidate or constraint keys)

Types of Cardinal Relationships among data.

1-One to One

2-One to Many

3-Many to Many

let's take the example of class and students

A class can have many students while a student can have only one class

so here is Many to One relationship.

Let's practice these by reading the below diagram.

A broker can have many transactions but a transaction can have only one broker.

A customer can have many transactions but a transaction can have only one customer

Now let's read the below Erd diagram

a productline can have many products while a product can have only one productline

a product can have many product orders while an order_product can have only one product

a customer can have many orders while an order can have only one customer

a customer can have many payments while a payment can have only one payment

an office can have many employees while an employee can have only one office

Reference:

https://www.visual-paradigm.com/guide/data-modeling/what-is-entity-relationship-diag