Post on 16-Jul-2015
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