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WELCOME TO MY
PRESENTATION
NAME: MD . IMRAN HOSSAIN
ID:152
SEC : PC -B
TopicEntityRelationship Diagram
(ERD)
IN 1967 PETER CHENDEVELOPED THE ER MODEL.
IT IS A HIGH LEVEL DATA MODEL USED FOR DEVELOPING THE
CONCEPTUAL DESIGN OF THE DATABASE.
COMPONENTS OF AN ERD
An ERD
consists of
four
componen
ts
Entity
Relationship
Cardinality
Attributes
Entity relationship diagram (erd)
TYPES OF RELATIONSHIP
 Unary Relationship: between two instances of one
entity type.
Student
Cheats
from
Binary Relationship : between the instances of
two entity types.
Teacher Teaches Subject
Ternary Relationship : Among the instances
of three entity types
CARDINALITY EXAMPLE
SCHOOL
STUDENT
Each school enrolls
at least zero
andat most many
students
Each student attends
at least one
andat most one
school
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
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
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
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
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
Entity relationship diagram (erd)
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.
ERD WITHCARDINALITY
Employee
Supervisor
Project
• Employee Name
• Employee No.
• Supervisor Name
• Supervisor No.
• Project Name
• Project No.
Department
Department Name
ATTRIBUTES
ROUGH ERD PLUS PRIMARY
KEYS
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
Entity relationship diagram (erd)

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Entity relationship diagram (erd)

  • 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.
  • 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