Customer–Order Relationship in Online Item Order System

Customer–Order Relationship in Online Item Order System

Customer Order relationship, Online Item Order System ER Diagram, One-to-Many relationship example, Database design Customer Order, Primary key foreign key example

📌 Question

In an Online Item Order System, two entities are identified: Customer and Order.

  • Is there a relationship between these two entities?
  • What type of relationship exists?
  • How is the primary key of the relationship (or related entity) formed?
  • Justify your answer considering real-world business rules and database design principles.

✅ Answer

1. Relationship Between Customer and Order

Yes, there exists a relationship between the Customer and Order entities. A customer can place one or more orders, and each order must be associated with exactly one customer.

2. Type of Relationship

The relationship is a one-to-many (1:N) relationship:

  • One Customer can have many Orders.
  • Each Order belongs to only one Customer.

3. Formation of Primary Key in the Relationship

- Customer primary key: Customer_ID
- Order primary key: Order_ID
- Relationship formation: Include Customer_ID as a foreign key in the Order table referencing Customer(Customer_ID). 

Customer(Customer_ID, Name, Contact, Address, ...)
Order(Order_ID, Order_Date, Total_Amount, Customer_ID [FK])

4. Justification

  • Ensures referential integrity so no order exists without a valid customer.
  • Models the real-world rule: a customer can place multiple orders, each order belongs to a single customer.
  • Including Customer_ID as a foreign key avoids redundancy and maintains a normalized database design.

5. ER Diagram Representation (Text Version)

Customer (Customer_ID, Name, Contact, Address)
        |
        | 1 --- ∞
Order (Order_ID, Order_Date, Total_Amount, Customer_ID [FK])

📌 Summary

  • One-to-many relationship exists between Customer and Order.
  • Primary key of Customer is Customer_ID, primary key of Order is Order_ID.
  • Foreign key Customer_ID in Order links orders to customers.
  • This design enforces referential integrity and reflects real-world business rules.

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