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We use ER Model for logical representation, which means If we want to see the Conceptual view of the data, so for that we use the ER Model.

It means, for any work, like If we need to build a building. Then before building a building, it is not like you directly call the builder and start making the building, No, before that we need to make a design or basic model from Architecture. So that whatever our requirements, the Architecture will design everything as per the requirement and we will give this design to the builder to make that building according to the requirement and that builder will have the basic idea that what is the requirement. If we do not prepare the basic model of the building and in the middle, If something gets wrong while making the building then we need to break that part or the whole building because according to our requirement, it is not being fulfilled. It means, it is a very big flaw.

In terms of Computer Science, If we are running an organization and, if we are designing a website or designing a database for a third party, we will prepare a conceptual model and will give that model to the implementation team who actually does coding, and then they will design a database and actually who fulfills those requirements. This is Entity Relationship Model or called as ER Model.

What does Entity mean?

It means, any object which has a physical existence that is known as Entity, means to say if talk about a Student, what can be a student?
Student can be an Entity and we represent the student entity with a Rectangle.
ER Model-1

What are the attributes of a student?

It means it can be the characteristics of a student. Like: Roll number, Age, and Address of the student. All these are the properties of the student or attributes or characteristics of the student and the student is an Entity.
ER Model-2

What is the Entity?

Entity means anything or any object which has some physical existence.
ER Model-3

What does a Relationship mean?

Any relationship or association between two or more entities, we call it relationship.
Example:
Let’s say there is an entity, a student. And we represent one Entity as a Student and the other as a Course. The course also has some attributes and characteristics, and what could be the course Characteristics? It can be the Course id, Course name, or course duration.

The relationship between the student and the course is study. What does a student do with the course? Students do the study, so there is a relationship between students and study and we can give the name of the relationship as Study and we represent the relationship with the Diamond.
ER Model-4

Actually, ER Model is a very simple model. We are not implementing it anywhere, it is just you can say, we have to do representation with a diagram or in a diagrammatic way.
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The whole structure we can call as Entity Type or Schema. This is a structure in which the student is an Entity and Roll No, Age, and Address are their attributes.
Similarly, there can be another such Entity, like we have taken here Course. And in Course Entity there can be the attributes like Course ID, Course Name, and Course duration. The relationship between them is called an Association or called as a Relationship.
This is just a conceptual view, a logical representation but further, we can implement it using SQL (Structure Query Language). So that we can actually give the user some designs at the backend.
Whatever e-commerce website we use in today’s time, the database was designed and implemented somewhere at the backend. From the front end, you have access to that database through an interface.

In this ER Model, what is Entity?

Entity is anything that is an object and which has a physical existence and we represent it with a Rectangle.

What is an Attribute?
Attribute means characteristics of the Entity and we represent the attributes with the Eclipse.

Relationship
We represent the relationship with the Diamond
ER Model-6

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