This presentation introduces entity relationship diagrams (ERDs). The key points are: - ERDs were developed by Peter Chen in 1967 as a high-level data model for conceptual database design. - The four main components of an ERD are entities, relationships, cardinality, and attributes. - Examples of relationship types are unary, binary, and ternary relationships. - Cardinality specifies the minimum and maximum number of relationships between entities. - Attributes provide descriptive properties for each entity.

1. WELCOME TO MY
PRESENTATION

2. NAME: MD . IMRAN HOSSAIN
ID:152
SEC : PC -B
TopicEntityRelationship Diagram
(ERD)

3. IN 1967 PETER CHENDEVELOPED THE ER MODEL.
IT IS A HIGH LEVEL DATA MODEL USED FOR DEVELOPING THE
CONCEPTUAL DESIGN OF THE DATABASE.

4. COMPONENTS OF AN ERD
An ERD
consists of
four
componen
ts
Entity
Relationship
Cardinality
Attributes

6. TYPES OF RELATIONSHIP
 Unary Relationship: between two instances of one
entity type.
Student
Cheats
from

7. Binary Relationship : between the instances of
two entity types.
Teacher Teaches Subject

8. Ternary Relationship : Among the instances
of three entity types

9. CARDINALITY EXAMPLE
SCHOOL
STUDENT
Each school enrolls
at least zero
andat most many
students
Each student attends
at least one
andat most one
school

10. ATTRIBUTES
Descriptive properties possessed
by each member of an entity set.
Example of entity types
and associated
attributes :
Student: Student_name
Employee: Employee_age
Event: Event_location

11. Student
Name Gender Class
Roll
number
Age
Primary Key: An attribute that has
been selected as the unique
identifying characteristic for an entity
type.
Example:
Student:Student_rollnumber
Staff:Staff_Id

12. A SIMPLE EXAMPLE
A company has several departments. Each
department has a supervisor and at least one
employee.Everysupervisorhasonlyonedepartment
underhim.Employeesmustbeassignedtoatleast
one,butpossiblymoredepartments.Atleastone
employeeisassignedtoaproject,butanemployee
maybeonvacationandnotassignedtoanyprojects.
Theimportantdatafieldsarethenamesofthe
departments,projects,supervisorsandemployees,
aswellasthesupervisorandemployeenumberand
auniqueprojectnumber.
A company has several departments. Each
department has a supervisor and at least one

13. employee. Every supervisor has only one department
under him Employees assigned must be at 0 or at least
one, but possibly more departments. At least one
employee is assigned to a project, but an employee
may be on vacation and not assigned to any projects.
The important data fields are the names of the
departments, projects, supervisors and employees, as
well as the supervisor and employee number and a
unique project number.
A true entity should have more than one instance

14. A Department is assigned an employee
A Department is run by a supervisor
An employee belongs to a department
An employee works on a project
A supervisor runs a department
A project uses an employee

16. FILL IN CARDINALITY
 Supervisor
 Each department has one supervisor.
 Department
 Each supervisor has one department.
 Each employee can belong to one or more departments
 Employee
 Each department must have one or more employees
 Each project must have one or more employees
 Project
 Each employee can have 0 or more projects.

17. ERD WITHCARDINALITY

18. Employee
Supervisor
Project
• Employee Name
• Employee No.
• Supervisor Name
• Supervisor No.
• Project Name
• Project No.
Department
Department Name
ATTRIBUTES

19. ROUGH ERD PLUS PRIMARY
KEYS

20. FULLY ATTRIBUTED ERD
Department
Is
Assign
Supervisor
Employee ProjectWorks
On
Runs
By
Departme
nt Name
Project
Name
Project
Number
Employee
Number
Supervisor
Number
Supervisor
Name
Employee
Name