This content originally appeared on DEV Community and was authored by Bellamer
What is an ER Diagram?
An Entity-Relationship (ER) Diagram is a visual representation of the entities in your database, their attributes, and the relationships between them. It serves as a blueprint for designing your database.
Key Components of ER Diagrams
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Entities: Represent real-world objects or concepts (e.g., Users, Orders).
- Depicted as rectangles.
-
Attributes: Describe the properties of an entity (e.g., Name, Email).
- Depicted as ovals connected to entities.
-
Relationships: Show how entities are related (e.g., Users place Orders).
- Depicted as diamonds between entities.
Example: Online Store ER Diagram
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Entities:
- Users (attributes: UserID, Name, Email)
- Orders (attributes: OrderID, OrderDate, Amount)
- Products (attributes: ProductID, ProductName, Price)
-
Relationships:
- A User can place multiple Orders.
- An Order can contain multiple Products.
[Users] ----< Places >---- [Orders] ----< Contains >---- [Products]
How to Design an ER Diagram
- Identify entities and their attributes.
- Define relationships and their cardinality (e.g., one-to-many, many-to-many).
- Normalize the structure to reduce redundancy.
ER Diagram in Action
Scenario: Design an ER Diagram for a Library System.
Entities: Books, Members, Loans.
-
Relationships:
- A Member can borrow multiple Books.
- Each Loan is associated with one Book and one Member.
Example Attributes:
- Books: BookID, Title, Author.
- Members: MemberID, Name, Email.
- Loans: LoanID, LoanDate, ReturnDate.
Challenge: Design Your Own ER Diagram
Scenario: Create an ER Diagram for a University System with the following entities:
- Students: Includes StudentID, Name, and Major.
- Courses: Includes CourseID, CourseName, and Credits.
- Enrollments: Tracks which students are enrolled in which courses.
- Draw the relationships. Are they one-to-many or many-to-many?
- What attributes should be stored in each entity?
Think About It
Why are ER Diagrams a critical step before creating a database?
How do you handle many-to-many relationships in an actual database schema?
This content originally appeared on DEV Community and was authored by Bellamer
Bellamer | Sciencx (2025-04-13T08:00:00+00:00) Entity-Relationship (ER) Diagrams: Visualizing Your Database Structure. Retrieved from https://www.scien.cx/2025/04/13/entity-relationship-er-diagrams-visualizing-your-database-structure/
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