Entity Relationship model (ER model)

The entity-relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects.
An entity is a “thing” or “object” in the real world that is distinguishable from other objects. For example, each person is an entity, and bank accounts can be considered as entities.
A relationship is an association among several entities. For example, a depositor relationship associates a customer with each account that she has.
The set of all entities of the same type and the set of all relationships of the same type are termed an entity set and relationship set, respectively.
The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram.

Component of E-R model

The E-R model consist of the following major components:

An entity is a class of persons, places, object, events or concepts about which we need to collect and store data.
Each entity is distinguishable from the other entities.
categories of different entities include:

An attribute is a descriptive property or characteristic of an entity.
Same attribute can be logically grouped into super attributes called compound attribute.

Key attribute is an attribute that uniquely identifies an entity in the entity set.