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Home » DBMS

Introduction of ER Diagram/ER Modelling



Learn- In this article we study about the introduction of Entity Relationship Diagram(ER Diagram). We understand why we use ER Diagram in Database management system? What are the basic attribute of ER Model.
Submitted by Prerana Jain, on April 30, 2018

The Entity Relationship Diagram is used to understand the relation of different entity (objects ortables) in the database. ER Diagram helps us to Understand the structure of back-end. It is a part of software that how we are going to design our database.

ER Diagram was introduced by Dr.Peter Chen in 1976.It is a database model based on the perception of real world that consist of Collection of basic objects and relationship between them. It is a non-technical method which is free from ambiguity. It provides a standard and logical way of organising and visualising a data. This model maps the real-world things into a conceptual schema. The conceptual schema is a concise description of data requirement. These concepts do not include implementation details and are easier to understand and commercialize for non-technical users.

E R Model Basics

There are the three basic elements in ER Diagram,

  1. Entity, Entity Set
  2. Attributes
  3. Relationships

1) Entity

An object is called entity if it can be identified in a group of objects based on the values of the attribute it processes.

Entity can be of two types

  • Tangible
  • Intangible

Tangible are those type of entity which exist Physical existence in the nature.

Example: A Bank locker, person, car etc.

Intangible are those type of entity which exist Logically in the nature.

Example: A Bank account, Job Company etc.

Collection of similar type of entity is called entity set. In ER Diagram entity is a instance and it is represented as a rectangular box while in a relational model it is represented by independent tables. Entity set is associated with the set of attributes.



2) Attributes

Attributes are the properties on which we can define entities. In ER Diagram they are represented by an oval or ellipse while in a relational model they are represented by independent column.

Types of attribute

1) Composite and single(Atomic) Attributes

The attributes which can be further divided into smaller attribute then it is called composite attribute.

Example: Address can be divided into city, state,country.

The attributes which cannot be further divided are called simple or atomic attributes.

Example: Age

In an E R Diagram composite attribute represented when an oval is connected to an oval.

2) Single valued and multivalued Attributes

Attributes which having a single value at any instant of time is called single valued attribute.

Example Gender

Attributes is to be multivalued if it can take more than one values at a time.

Example Phone no, Address no.

3) Stored and derived attribute

Attribute is said to be stored if its value is permanently stored in the database.

Example Date of birth.

The Attributes whose value is derived or calculated at run time the it is called derived attribute.

Example Age can be derived from the date of birth.

3) Relationship

Relation specify that how a entity of a entity set is related to the entity of another set. In a ER Diagram it is represented by a diamond. Every relationship will have a unique name.

Every relationship will have a degree which means no of entity set participating.






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