Entity Relationship Diagram.pptx

8/18/2019 Entity Relationship Diagram.pptx

1/17

Entity Relationship Diagram

Rani Mohanlal Assistant ProfessorDept. of CSE VAST


2/17

Table of Contents

Introdution

ERD omponents

• Entity

• Attribute

• Relationship

Cardinality onstraints

• !ne " to " one

• !ne " to # many

• Many " to " one

• Many " to " many

Partiipation onstraints

• Total

• Partial

$ea% entity set


3/17

ER Diagram

ERD is a tool for designing databases

Peter P. Chen proposed the ER model in &'()

Coneptual data model

*ie+s the real +orld as a set of entities and

relationships,assoiations bet+een these entities.


4/17

ERD Components

Primary Components of ERD

Entity

Attribute

Relationship


5/17

ERD Components Contd.

Entity

Distinguishable ob-et person/ plae/ thing/ e*ent or ob-et0 about +hih information is stored.

E1ample2" employee/ department.Entity Set2" Set of entities of same type that share same properties,attributes.

Classifiation• Physial

• Abstrat

• Independent

• Dependent

employee

department


6/17


Attributes

Properties of entity . Eah attribute has a domain.

E1ample2" employeeemp. no./ name/ dept/ desig/ D!3/ age0

employee

emp4no

namedept

desig.

D!3

f4name l4nameDomain eg.

Age5677/78/"""/99:name5 haraterstring of length &9

Phone no


7/17

Attributes Contd.

Classifiation• ;ey and


8/17


Relationship

Assoiation among t+o or more entitiesDegree of a relationship


9/17

E1ample sho+ing a binary relationship

Employee

Department $or

%s4f or

Phone

D!3

Address Dept4id


10/17

Cardinality Constraints

Cardinality

Atual no. of related ourrenes for eah of the t+o entities.

Types

A 3 A 3 A 3 A 3

&"to"& &"to"Many Many"to"& Many"to"Many


11/17

Cardinality E1amples&2& >


12/17

Cardinality E1amples&2< >


13/17

Partiipation Constraint

An entity set may partiipate in a relation either totally or partially.

• Total Partiipation2" E*ery entity of an entity type is related to someother entity set *ia a relationship type.

• Partial Partiipation2" If only fe+ members of an entity type is relatedto some other entity set *ia a relationship type.

E& E7R

Total Partial


14/17

Total,partial partiipation e1amples

Professor Studentguide


15/17

$ea% entity

$ea% entity2"

• an be identified uni=uely only by onsidering the primary %ey ofanother owner0 entity.

• !+ner entity set and +ea% entity set must partiipate in a one"to"many relationship set.

• $ea% entity sets must ha*e total partiipation in this identifyingrelationship set.

S $ R

!+ner entity $ea% entity

Al+ays Total


16/17

$ea% entity set e1ample

CourseSetion@as

Setion


17/17

E1ample

Employee

Department

Pro-et

name

emp 4no

deptD!3

+or% s4on

+or%s 4for

P4no.

P4name. budget

dep4no.dep4na

me

loation

&

<

M

Entity Relationship Diagram.pptx

Documents