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ENTITY RELATIONSHIP MODEL:

Definitions and introduction:

ENTITY RELATIONSHIP (E-R) MODEL is basically a non-technical design method that is employed for the conceptual model of database design. This traditional approach concentrates on the database structures and underlying constraints during conceptual database design. This model focuses on real-world objects and the relationships among those objects.

As per abstraction level first, we go for high level or Conceptual design then Relational table then Physical store or database.

Basic Concepts:

The E-R model comprises three basic terms- Entity set, Relationship Set, and Attributes.

Entity – An entity is a “thing” or “object” in the real-world that can be distinguished from any other objects, i.e, Entity has a completely independent existence. Based on the existence, Entity can be classified into two categories:-

a. Concrete- Entities that exist physically. For example, Phone, Pen, Person, etc.

b. Abstract- Entities that exist logically. For example, Holiday, Account, Course, etc.

Attributes – Property of object (Name, age, etc)

Relationship – Association (Work for)

How to differentiate entity, attributes, and relation from client requirement (SRS):

We first collect information from the client and convert conversation/information into the diagram.

Generally, we extract ‘noun’ from information/conversation as an object called entity. Like a person, employee, manager, car.

Characteristics of a noun are called attribute of this entity.  Like a person has fname, lname, address, ph_no. etc.

And ‘verb’ as a relationship like A person owns a car. An employee works for a department. Here owns and works are relationship.

Now, 

Name or heading is called entity type and the element of the entity type is an entity. Sometimes entity type is called intension and entity is called extension.

Attributes describe an entity and by more attributes, we can describe an entity in better ways.