2. ER model stands for an Entity-Relationship model. It is a high-level data
model. This model is used to define the data elements and relationship for
a specified system. It develops a conceptual design for the database. It also
develops a very simple and easy to design view of data.
3. INDEX
1. INTRODUCTION
2. ENTITY
3. ATTRIBUTES
4. TYPES OF ATTRIBUTE
I. SINGLEVALUE AND MULTIVALUE
II. SIMPLE AND COMPOSITE
III.BASE AND DERIVE VALUE
IV.NULL VALUE
4. INTRODUTION
• The entity relationship model is based on
the real word which consist of a set of
objects.
• The basic objects are called entities
• The properties of the entities are known as
attributes.
• There must be a relationship between the
two entities.
5. 2.ENTITY
• An entity is an object or thing or a person
which can be distinguished with the help of
its attributes.
• Entity is an important factor of any
organization .
• The organization can have any number of
living and non-living objects.
• These objects are known as entities.
• Examples of entity are-student, college,
6.
7. 3.ATTRIBUTES
• Each entity of the entity set is identified
by the properties or characteristics.
• These properties of the entity set are
known as attributes.
• There may be a number of attributes in
any entity.
• Most of them may be at least one
property which identifies the entities.
8.
9. 4.TYPES OF ATTRIBUTES
I. SINGLEVALUE AND MULTIVALUE
II. SIMPLE AND COMPOSITE
III.BASE AND DERIVE VALUE
IV.NULL VALUE
10. SINGLEVALUE AND MULTIVALUE
SINGLEVALUE :-
• The attributes which can contain maximum one and
minimum one value are known as single attribute.
• Example:- roll no, enrollment no etc.
MULTIVALUE:-
• The attributes which can contain more than one
value of a time are known as multi value attributes.
• Multi values are represented by double ovals.
• Example:- contact no.
11. SIMPLE AND COMPOSITE
SIMPLE ATTRIBUTES:-
• The attributes which cannot be divided are
examples of simple attributes.
• Example:-enrollment no, roll no etc.
COMPOSITE ATTRIBUTES:-
• The attributes which can be of further
classified are known as composite
attributes.
• Example:-address of a student can be
further divided into Q. no, street no, postal
no etc.
12. BASE AND DERIVE VALUE
BASE ATTRIBUTES:-
• The attributes where value is a compulsion are
known as base attributes .
• Example:-DOB.
DERIVED ATTRIBUTES:-
• These are the attributes for which the value is
calculated using base attributes of some operations
• Derive values are represented by dotted oval.
• Example:- Age can be calculated using the base
value date of birth.
13. NULL VALUE
• Normally every attribute takes values
from the range of values but there may be
cases where its not possible to insert
values every time.
• The situation is handled using special
type value “NULL”.
