The document discusses entity relationship diagrams (ERDs), which are modeling tools used to graphically depict a database design before implementation. An ERD has three basic components: entities, relationships, and attributes. Entities represent real-world objects like people, places, or concepts. Relationships show how entities relate to each other and are depicted as verbs or nouns connecting entities. Attributes provide additional information about entities and relationships, such as names, IDs, and dates. The document provides examples of entities, relationships, and attributes in ERDs.

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Entity RelationshipEntity Relationship
DiagramDiagram

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ERD (Entity Relationship Diagram)ERD (Entity Relationship Diagram)
►is modeling tool used to depict graphically ais modeling tool used to depict graphically a
database design before it is actuallydatabase design before it is actually
implemented.implemented.
►It has three basic components, namely, anIt has three basic components, namely, an
EntityEntity,, RelationshipRelationship and anand an AttributeAttribute..

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EntityEntity
► is a real-world object distinguishable or uniqueis a real-world object distinguishable or unique
from other objects.from other objects.
► An entity can be aAn entity can be a concreteconcrete oror physicalphysical objectobject
likelike employeeemployee,, studentstudent,, facultyfaculty,, customercustomer etc. Or itetc. Or it
could also becould also be conceptualconceptual oror abstractabstract likelike
transactiontransaction,, orderorder,, coursecourse,, subjectssubjects etc.etc.
► It can be thought of as a noun likeIt can be thought of as a noun like student,student,
employeeemployee etc.etc.
► It is normally represented by a rectangle shape.It is normally represented by a rectangle shape.

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RelationshipRelationship
►is a way of relating one entity to another.is a way of relating one entity to another.
Entities can therefore participate in aEntities can therefore participate in a
relationship.relationship.
►it is commonly thought as ait is commonly thought as a verbverb connectingconnecting
thethe entitiesentities oror nouns.nouns.
►It is normally represented by a diamondIt is normally represented by a diamond
shape.shape.

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Example of Entities with RelationshipExample of Entities with Relationship
Person belongs Location
Student enrolls Subject(s)
Faculty teaches Subject(s)

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Types of RelationshipTypes of Relationship
►One-to-OneOne-to-One
►One-to-ManyOne-to-Many
►Many-to-ManyMany-to-Many

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Types of RelationshipTypes of Relationship
Student has ID
Division has Program
Student enrolls Subject
1 1
1 M
MM
One-to-One
One-to-Many
Many-to-Many

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Types of Relationship (CrowTypes of Relationship (Crow
Notation)Notation)
Student has ID
Division has Program
Student enrolls Subject
One-to-One
One-to-Many
Many-to-Many

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AttributeAttribute
► Refers to the characteristic or basic fact or field ofRefers to the characteristic or basic fact or field of
an Entity or Relationship.an Entity or Relationship.
► For example a Student entity could have theFor example a Student entity could have the
followingfollowing attributesattributes ID NumberID Number,, Last Name, FirstLast Name, First
Name, Address, Birth DateName, Address, Birth Date etc.etc.
► A relationship could also have an attribute forA relationship could also have an attribute for
example an Entity nameexample an Entity name StudentStudent enrollsenrolls
(relationship) to a(relationship) to a Course/ProgramCourse/Program. Now, when. Now, when
you enroll you enroll on a certain date so you willyou enroll you enroll on a certain date so you will
have an attribute ofhave an attribute of Enrollment DateEnrollment Date underunder EnrollEnroll
relationship.relationship.
► It is normally represented by aIt is normally represented by a circlecircle..

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Example of AttributesExample of Attributes
Student
ID No.
Lastname Firstname
Gender
Address
Birth date
Email
Note : A Primary Key is Underlined, in this case the ID No.

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Example of AttributesExample of Attributes
Student
ID No.
Lastname Firstname
Gender
Address
Birth date
Email
enrollsProgram
Enrollment
Date
Program ID
Name
Chairperson
has Faculty
ID No.
Lastname
Firstname

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Example of AttributesExample of Attributes
Student
ID No.
Lastname Firstname
Gender
Address
Birth date
Email
enrollsProgram
Enrollment
Date
Program ID
Name
Chairperson
has Faculty
ID No.
Lastname
Firstname

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Recursive ERDRecursive ERD
Employee
manages

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ERD with Ternary RelationshipERD with Ternary Relationship
Supplier supplies Product
Customer

15. © 2007 by Prentice Hall Management Information Systems, 10/e
Raymond McLeod and George Schell
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ERD (More Examples)ERD (More Examples)

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ERD (More Examples)ERD (More Examples)
Employee
Project
Department
Branch
Manages
Is_a_Member
Participates has
Code
Name
Age
Salary
Start Date
Name
Budget
Release Date
Start Date
Name
Dept ID
City
Address