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โ›“ Entity Relationship modelling (ERD)

A type of diagram that lets you see how different entities (e.g. people, customers, or other objects) relate to each other in an application or a database.

It's used to represent data in a given scenario.
Entity relationship models have 3 components:
- Entities
- Attributes
- Relationships


An entity is something in the real world that can be represented in the system. These could be: books, people, a bag etc...
Each entity is represented by a rectangular box with its name written inside it.
The information held on an entity is a set of characteristics that define the entity. These are known as attributes
The relationship between the entity, attributes and other entities are the relationships.

Degree of the relationship#


One to One This is when something is directly linking to something else.



One to Many
When something is linking to multiple other things



Many to Many
This is where any things link with many things