ER Diagram
What is an ER Diagram?
ER Diagram stands for Entity-Relationship Diagram. It is a visual representation of the data and its relationships in a database.
Why do we use an ER Diagram?
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To design or model the database structure before creating it.
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To understand how different entities (things) relate to each other.
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Helps in planning and communicating the database design clearly.
What does "Draw ER diagram for given problem" mean?
It means:
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You are given a description of a system or scenario (the "problem").
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You need to identify the entities, attributes, and relationships from that description.
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Then draw a diagram showing:
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Entities as rectangles,
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Attributes as ovals connected to entities,
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Relationships as diamonds connecting entities,
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And lines showing how entities are linked.
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Example: Simple ER Diagram for a Library System
Problem Statement:
A library has Books and Members. Members can borrow multiple books. Each book has a title and author. Each member has a member ID and name.
Entities:
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Book
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Member
Attributes:
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Book: BookID, Title, Author
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Member: MemberID, Name
Relationship:
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Borrow (between Member and Book)
How ER Diagram looks:
[Member]------(Borrow)-------[Book]
|MemberID |BookID
|Name |Title
|Author
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Rectangles: Member, Book
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Diamond: Borrow (relationship)
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Ovals: Attributes like MemberID, Name, Title, Author (usually drawn connected to entity rectangles)
Example : Simple Student-Course ER Diagram
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Entities: Student, Course
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Relationship: Enrolls
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Attributes:
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Student: StudentID, Name
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Course: CourseID, Title
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Relationship connects Student and Course
Example : Library System
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Entities: Book, Member, Librarian
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Relationships:
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Member borrows Book
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Librarian manages Book
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Attributes:
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Book: ISBN, Title, Author
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Member: MemberID, Name
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Librarian: EmployeeID, Name
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Example : Hospital Management
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Entities: Patient, Doctor, Appointment
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Relationships:
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Patient has Appointment
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Doctor conducts Appointment
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Attributes:
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Patient: PatientID, Name, Age
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Doctor: DoctorID, Name, Specialty
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Appointment: Date, Time
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Example : Online Shopping
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Entities: Customer, Order, Product
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Relationships:
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Customer places Order
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Order contains Product
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Attributes:
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Customer: CustomerID, Name
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Order: OrderID, Date
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Product: ProductID, Name, Price
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Example : University Database
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Entities: Student, Professor, Department
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Relationships:
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Student registered in Department
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Professor works in Department
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Attributes:
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Student: StudentID, Name
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Professor: ProfID, Name
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Department: DeptID, Name
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Example : Airline Booking System
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Entities: Passenger, Flight, Booking
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Relationships:
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Passenger makes Booking
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Booking is for Flight
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Attributes:
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Passenger: PassengerID, Name
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Flight: FlightID, Source, Destination
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Booking: BookingID, Date
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Example : Banking System
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Entities: Account, Customer, Transaction
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Relationships:
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Customer owns Account
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Account has Transaction
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Attributes:
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Account: AccountNo, Balance
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Customer: CustomerID, Name
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Transaction: TransactionID, Amount, Date
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Example : School Management
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Entities: Teacher, Class, Student
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Relationships:
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Teacher teaches Class
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Student attends Class
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Attributes:
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Teacher: TeacherID, Name
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Class: ClassID, Subject
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Student: StudentID, Name
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Example : Movie Database
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Entities: Movie, Actor, Director
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Relationships:
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Actor acts in Movie
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Director directs Movie
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Attributes:
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Movie: MovieID, Title, ReleaseYear
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Actor: ActorID, Name
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Director: DirectorID, Name
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Example : Hotel Reservation
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Entities: Guest, Room, Reservation
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Relationships:
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Guest makes Reservation
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Reservation includes Room
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Attributes:
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Guest: GuestID, Name
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Room: RoomNo, Type
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Reservation: ReservationID, Date
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Note
ER diagrams help visualize data and how different entities relate to one another. Each example involves identifying entities, their attributes, and the relationships connecting them.