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Last Updated On: July 2, 2017
Editor: Adeeb C

ER Model Tutorial – Concepts of Entity, Attribute, and Relationship

Category: DBMS,Programing
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Are you searching for ER Model Tutorial? Here I’m describing the concepts of ER Model, Entity, Attribute, and Relationship.

ER Model Tutorial

ER Model (Entity-Relationship Model) is a conceptual data model in DBMS. The ER model is very useful in mapping the meaning and interactions of real world enterprises onto a conceptual schema.

Concepts of ER Model

There are three basic concepts in Entity-Relationship model. They are:

  1. Entity Sets
  2. Relationship Sets, and
  3. Attributes

 

Entity Sets

  • An entity is a thing or object in the real world that is distinguishable from all other objects.

Example: Each student in a school.

  • An entity set is the set of entities which share the same properties.

Example: The collection of all students in the school. Where all of the students should have properties like admission_no, name, address and date_of_birth.

 

Relationships

  • A relationship is an association among several entities.

Example: Consider the example of student and project. Here the student work on the project. So the relationship in this relation is “work_on”.

 

Attributes

  • Attributes are the properties of entity.

Example: The entity student has the properties like admission_no, name, address and date_of_birth.

  • The collection of values of an attribute is known as value set or domain.

Example: The collection of all admission numbers from the database of a school.

Categorization of Attributes

The attributes can be mainly categorized into four groups. They are described below.

 

Simple v/s Composite Attributes

  • Simple attributes cannot further be divided into sub parts (sub attributes).

Example: The attribute phone cannot further be divided.

  • Composite attributes can be further divided.

Example: The attribute name can further be divided into sub parts like first_name, middle_name, and last_name.

 

Single Valued v/s Multi Valued Attributes

  • The attribute that can have only one single value is called Single valued attribute.

Example: The attribute date_of_birth can have only one value.

  • The attribute that can have multiple values is called Multi valued attribute.

Example: The attribute phone_no can have multiple phone numbers.

 

Derived v/s Stored Attributes

  • The Stored attributes are the attribute that have a direct value stored.

Example: The attribute date_of_birth has a direct stored value.

  • The Derived attributes are the attributes that doesn’t have a direct values, but the values are derived from stored attributes.

Example: The attribute age is derived from the date_of_birth attribute.

 

Null Attributes

  • A particular entity may not have a applicable value for an attribute. This type of attributes are called Null Attributes.