This document provides an overview of entity relationship (E-R) modeling concepts for database design. It defines entities, attributes, relationships, and E-R diagram notations. It describes the different types of entities, attributes, and relationships like weak entities. It also covers advanced concepts like generalization, specialization, and aggregation. The document is presented by 5 students and contains references for further reading.

1. Entity Relationship
(E-R) Model
Database Management System
Date – 20/04/2019
RAMKRISHNA MAHATO GOVERNMENT
ENGINEERING COLLEGE
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2. Presented by:
NAME ROLL NO.
1.SHILPA DE 35000116019
2.SAYAN DAS 35000116021
3.SANJIT MONDAL 35000116022
4.SAIKAT PAL 35000116023
5.ROHIT MAHATO 35000116024
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3. Contents
 Entity
 Attribute
 Classes of attributes
 Relationships
 Relationship Constraint
 Weak Entity
 Notations for ER Diagram
 Specialization
 Generalization
 Aggregation
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4.  E-R Model Components
 Entities
 In E-R models an entity refers to the entity set.
 An entity is represented by a rectangle containing the
entity’s name.
 Attributes
 Attributes are represented by ovals and are connected to
the entity with a line.
 Each oval contains the name of the attribute it represents.
 Attributes have a domain -- the attribute’s set of possible
values.
 Attributes may share a domain.
 Primary keys are underlined.
 Relationships
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5. The Attributes of the STUDENT and CAR Entity
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6.  Classes of Attributes
 A Single-valued attribute can have only a single value.
 Examples:
 A person can have only one social security
number.
 A manufactured part can have only one serial
number.
 Multi-valued attributes can have many values.
 Examples:
 A person may have several college degrees.
 A household may have several phones with
different numbers
 Multi-valued attributes are shown by a double line
connecting to the entity.
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7. Splitting the Multivalued Attributes into New Attributes7

8.  Classes of Attributes
 A simple attribute cannot be subdivided.
 Examples: Age, Sex, and Marital status
 A composite attribute can be further subdivided to
yield additional attributes.
 Examples:
 ADDRESS Street, City, State, Zip
 PHONE NUMBER Area code, Exchange number
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address
Street city zip

9.  A derived attribute is not physically stored within the
database; instead, it is derived from stored attributes.
 Example: AGE can be derived from the data of birth and
the current date.
Figure: A Derived Attribute
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10.  A relationship is an association between entities.
 Relationships are represented by diamond-shaped
symbols like “ “
Figure :An Entity Relationship
Relationships10

11. Types of relationship:
 Unary relationship
 Binary relationship
 Ternary relationship
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12. One to One relationship:12
A
B
C
1
2
3

13. One to many relationship:13
A
B
P
Q
R
S

14. Many to many relationship:14
A
B
C
X
Y
Z
W

15. Unary Relationship
• Relationship between the instances of one entity
type.
Is_married_to Manages
PERSON
EMPLOYEE
One-to-one One-to-many
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16. EMPLOYEE
PARKING
SPACE
PRODUCT
LINE
PRODUCTS
Is_assigned
Binary Relationship
• Relationship between the instances of two entity type.
Contains
One-to-One
One-to-Many
1 M
1 1
Can also have many to many!
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17. Ternary Relationship
• A simultaneous relationship among instances of
three entity types.
EMPLOYEE
JOB
DEPARTMENTWorks_On
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18.  Cardinality
 Cardinality expresses the specific number of entity
occurrences associated with one occurrence of the
related entity.
Figure :Cardinality in an ERD
Relationship Constraints18

19. Cardinality Ratio Example
Student
Hostel
Room
Student
Resides
in
1 1
Address
N
a
m
e
Roll
Hostel
name
Room
no
professor
Depart-
mentBelongs
to
N 1
Name
Phone
No
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20. • Disjoint
• Completeness constraint (use double lines)
– total : an entity must belong to one of the lower-
level entity sets
– partial: an entity need not belong to one of the
lower-level entity sets
Participation20

21.  A weak entity is an entity that
 Is existence-dependent and
 Has a primary key that is partially or totally derived
from the parent entity in the relationship.
 The existence of a weak entity is indicated by a
double rectangle.
 The weak entity inherits all or part of its primary
key from its strong counterpart.
Weak Entities21

22. • Double rectangles for weak entity set
• Double diamond for weak entity relationship
• Dashed underscore for discriminator
Example
Weak Entity Set Notations22

23. Summary of Symbols Used in E-R Notation
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24. Super class and Sub class
entity type
 A super class is an entity type that
includes distinct sub classes.
 A Sub class is an entity type that has
a distinct roll and also a member of
super class
Advantages:
1.It eliminates the requirement of describing
Similar concepts more than once. Thus saving
Time from data modeling.
2. Add more semantic content and information
to the design
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25. EXAMPLE
Employee
Employee
No
Date of
joining
Name DOB
Address
Full Time Part Time Consultant
Salary Allowance Hourly
Rate
Contact
no
Billingrate
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26. Extended E-R Features: Specialization
• Top-down design process.
• A lower-level entity set inherits all the attributes and
relationship participation of the higher-level entity set
to which it is linked.
• A lower-level entity set may have additional attributes
and participate in additional relationships
• Depicted by a triangle component labeled ISA (E.g.
customer “is a” person).
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27. Specialization Example
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28. Extended ER Features: Generalization
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.
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29. 29
Generalization Example

30. 30 Components of the E-R Model

31. Aggregation
Consider the ternary relationship works_on
Suppose we want to record managers for tasks performed by an
employee at a branch
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32. Aggregation (Cont.)
Relationship sets works_on and manages represent
overlapping information
Every manages relationship corresponds to a works_on
relationship
However, some works_on relationships may not
correspond to any manages relationships
So we can’t discard the works_on relationship
Eliminate this redundancy via aggregation
Treat relationship as an abstract entity
Allows relationships between relationships
Abstraction of relationship into new entity
Without introducing redundancy, the following diagram
represents:
An employee works on a particular job at a particular
branch
An employee, branch, job combination may have an
associated manager
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33. E-R Diagram With Aggregation
Higher level
entity type
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34. References:
1.TEXTBOOK : Fundamentals of Database
System (PEARSON)
2. TEXTBOOK : Database System Concepts
(McGraw-Hill Education)
2. NOTEBOOK : PROF. PABITRA ROY
3. WEBSITE : www.google.com
4. www.youtube.com
5. nptel.ac.in
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