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Introduction to database management systems


Entity Relation Diagram Representation

ER-Diagram is a visual representation of data which describes how data is related to each other. There are few symbol used to represent the relationship between them.

ER diagram basics

 

Entity

An Entity can be any person, place, class or object. In E-R Diagram, an entity is represented using rectangles. Eg : In Organization Employee and Department are entity.

DBMS ER representation

Attributes

The Describing the property of an entity is called as Attribute. Eclipse is used to describe the entity. Eg : Age,Name are attribute of Entity.

DBMS attributes

Key attribute

Key attribute represents the main characteristic of an Entity. It is used to represent a primary key. Ellipse with underlying lines represent Key Attribute.

key attribute DBMS

 

Composite Attribute

An attribute that have their own attributes. These attributes are known as Composite attribute.

composite attribute

Relationship

A Relationship describes relations between entities. A Relationship is represented using diamonds.

relationships

There are 3 types of relationship which exist between Entities.

  • Binary Relationship
  • Recursive Relationship
  • Ternary Relationship

Binary Relationship

Binary Relationship means relation between two Entities. This is divided into three types.

  1. One to One: This type of relationship is rarely seen in real world.



    The above example shows that one student can enroll only for one course and a course will also have only one Student.

  2. One to Many: This reflects business rule that one entity is associated with many number of same entity. For example, Student enrolls for only one Course but a Course can have many Students.

    one to many relationships
    The arrows in diagram shows that one student can enroll for only one course

  3. Many to Many:

     

    many to many relation example

    The above diagram represents that many students can enroll for more than one courses.


Recursive Relationship

When an Entity is related with itself it is known as Recursive Relationship.

recursive relationship

Ternary Relationship

Relationship of degree three is called Ternary relationship.

Participation Constraints

  • Total Participation: each entity is involved in relationship. Total participation is represented by double lines.
  • Partial participation: Not all entities are involved in the relationship. Partial participation is represented by single lines.

Description

This free tutorial covers the basics of database management system to help you with your understanding on the topic, Please note that this tutorial assumes that either you are a beginner or just want to brush up your understanding on DBMS

Tutorial covers the topics below

  • What is DBMS?
  • Architecture
  • Data Models
  • Data Schemas
  • Data Independence
  • Entity-Relation Model Basic Concept
  • Entity-Relation Diagram Representation
  • Generalization, Aggregation
  • Codd's 12 Rules
  • Relational Data Model
  • Relational Algebra
  • Structured Query Language
  • Normalization
  • Database Joins
  • Storage System
  • Indexing
  • Hashing
  • Transaction
  • Concurrency Control and Deadlock
  • Data Backup and Recovery

 



Audience

Absolute beginners or students who wish to brush up their understanding on DBMSes

Author: Subject Coach
Added on: 16th Sep 2015

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