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Explain the E-R Model in RDBMS

In this tutorial, we are going to learn about the E-R Model in RDBMS and its key components.
Submitted by IncludeHelp, on November 08, 2020

ER model stands for entity relationship model. It is a logical model which portrays the logical design of a database with the help of a relationship diagram, which is known as Entity Relationship Diagram (ER Diagram). Before understanding this model very well, it is very important to know its components and the key components of ER model are as follows -

Entity

It is an object defined as table in the database which holds specific data in it. Table name in the database is treated as an entity. Each and every entity has their properties to define it, which also called its attributes. In ER diagram, an entity represents in rectangular box.

For example, in school database student table can be an entity.

Attributes

Attribute is a property of an entity. In ERD, attributes represents' in the Oval shape.

Attribute types - there are four types of attributes:

1. Key attribute
2. Composite attribute
3. Multivalued attribute
4. Derived attribute

Relationships

Relationship defined as the associations between related entities. In ER diagram, relationship is represented through diamond shape which shows the relationship among entities. There are four types of relationships:

1. One to One
2. One to Many
3. Many to One
4. Many to Many

The shapes used to make an ER diagram

Shape	Shape Name	Purpose
	Rectangle	Represents Entity sets
	Ellipse	Attributes
	Diamond	Relationship
	Lines	To link attributes to entity sets and entity sets to relationship set
	Double Ellipses	Multivalued attributes
	Dashed Ellipses	Derived Attributes
	Double Rectangles	Weak Entity Sets
	Double Lines	Total participation of an entity in a relationship set

Facts about ER Diagram Model:

• ER model facilitates to make database and its relational design
• It is a graphical representation for modeling data
• It is most widely used to design the logical structure of a database
• It helps to identify the entities and their relationships.