---
Video Title: Entity Relationship Model
Description: Entity Relationship Model
Watch more Videos at https://www.tutorialspoint.com/videotutorials/index.htm
Lecture By: Mr. Arnab Chakraborty, Tutorials Point India Private Limited
---

Entity relationship model is a topic in
this session.

We also call it as ER model.

Entity is something which has got an
independent existence in an enterprise.

And relationship means how the multiple
entities are getting related.

So, that is the origin of this entity
relationship model.

So, let us go for the detailing on this ER
model along with some examples.

So, entity relationship model is a type of
database model based on the notion of real

world entities and the relationships among
them.

So, real world entities,
I told you that entity

has
got some existence in the enterprise.

We can map real world scenario onto ER
database model.

ER model creates a set of entities with
their attributes and set of constraints

and relations among them.

With each and every entity, some set of
attributes are connected.

Depending upon the values of some attributes,
an entity can be identified uniquely.

So, whenever we are
having alike entities, then

collection of them
will form the entity set.

So, let us suppose, we are having one
student.

So, in our college admission system,
student is one entity.

One course is one entity.

One teacher's respective details will be
one entity.

So, in case of student
admission system or

say in case of college
administration system.

So, there we are having multiple entities
coming in that way.

So, with a particular student,
as student is one entity, So, role number,

name, age, gender, email address,
phone number, contact address and so on.

So, these are the different attributes are
there.

So, ER model is best used for conceptual
design of database.

And ER model can be represented as
follows.

Entities will be represented in the form
of a rectangle.

This attributes will be represented in the
form of ellipse.

And this relationships will be represented
in the form of this diamant.

And this lines are showing the links
between them.

So, here we are having two entities,
each one of them are having two attributes.

Obviously, it is not
mandatory that entities

connected should have the same number
of attributes.

It can have 5 attributes, it can have 50
attributes.

So, that is not a problem.

And this relationship is actually
connecting this entity and with that entity.

So, entity is an
entity in ER model is a real world being

and which has
some properties called the attributes.

And every attribute is defined by the
corresponding set of values called the domain.

So, domain is nothing but a set of values
from where you can pick up one value to

instantiate one attribute.

So, domain means actually the set of
values from where you can pick up one

value to initialize one attribute.

For example, consider a school database.

Here, a student is an entity.

Student has various attributes like name,
id, age and class, etcetera.

So, now, we are going for the
relationship.

That means, this one.

There is a diamond shaped box is there.

The logical association among entities is
called relationship.

So, relationships are mapped with entities
in various ways.

Mapping cardinality define the number of
associations between two entities.

So, here we can have the mapping
cardinality.

Actually, we are having basically four
different mapping cardinality that is one

to many, many to one, one to one and many
to many.

So, here we are having the respective
mapping cardinality.

We have described that one here.

So, now, let us go
for some example to explain

how this mapping
cardinality are working.

So, here we are having this one to many.

Whenever we are having one, there this
arrow will be coming.

Whenever we are having many, there will be
no arrow.

Consider this one many to one.

So, here many is having no arrow,
but one is having arrow.

So, that means, one customer can have
multiple number of loans.

And against one loan, there is only one
customer connected.

That means, this bank can provide multiple
parallel personal loans.

Because against one loan, there will be
one customer.

So, personal loan.

Against one customer, there will be
multiple loan numbers.

So, multiple parallel personal loans can
be provided.

So, consider this one.

Multiple customers against one loan.

So, against one
One customer, there will be one loan

against one
loan, there will be multiple customers.

That means, here it provides the joint
loan, there is a group loan, there is bank

issues, but a customer who is having one
of the loans cannot have the another

parallel loans, because it is many,
but it is one.

So, against one customer name,
there will be one loan against one loan

number, there will be multiple customers
name.

Now, let us consider this one as one So,
both sides arrows are there.

So, that is one to one.

So, it depicts that one customer can have
a single loan and only one loan at a time.

So, many to many means multiple customers
multiple loans.

So, that means that
this particular bank issues

parallel personal
loans or group loans at the same time.

So, in this way you have described what is
the entity relationship model with some

proper examples and what are the different
symbols we are going to use to represent

and to draw this entity relationship
model.