GANDHINAGAR INSTITUTE OF

TECHNOLGY

Department of Information Technology

E-R FeaturesGroup ID: IT_A1_10

Students Names: Akabari Nirali (130120116002)

Akanksha Sharma (130120116003)

Guided By: Prof. Anirudhdha Nayak

Database Management System(2130703)

Presentation outlines:

E-R concept

Specialization

Generalization

Aggregation

E-R diagram notation for representing

specialization

E-R diagram with redundant

relationship

E-R diagram with Aggregation

Basic E-R concepts

The original concept of the entity-

relationship model was given by Chen in

1976.

High level conceptual(logical) data

model.

Widely used in database design to

represent a conceptual schema.

A conceptual schema represented by the

E-R model is called an E-R schema.

The basic notation used in E-R

diagram are illustrated below:

An entity set

An Attribute

A Relationship set

Link between an

entity set &

attribute

Specialization

Specialization is the process of

defining sub-class based on some

distinguishing characteristics.

In other words, specialization identifies

the sub-sets possesses some

attributes

Specialization is a top-down process

to define super-class/sub-class

relationships.

Generalization

Generalization is the process of

defining a super-class from sub-

classes based on some common

characteristics.

In other words, generalization

identifies a super-class from different

entity-sets(or sub-classes).

Generalization is a bottom-up process

to define super-class/sub-class

relation.

A bottom-up design process – combine

a number of entity sets that share the

same features into a higher-level entity

set.

Specialization and generalization are

simple inversions of each other; they

are represented in an E-R diagram in

the same way.

The terms specialization and

generalization are used

interchangeably.

Aggregation

Aggregation is an abstraction through

which relationships are treated as

higher level entities.

Thus, for our example, we regard the

relationship set works on as a higher-

level entity set called works on.

Such an entity set is treated in the same

manner as is any other entity set.

Figure shows a notation for aggregation

commonly used to represent this

situation.

E-R Diagram With

Aggregation

E-R Diagram With

Redundant Relationships