Hello, experts, it\'s a question about Database system. Here is a question about

Question

Hello, experts, it's a question about Database system.

Here is a question about identifying binary relationships in the following relations

I'm confusing on the argument that the textbook provides:

It said in Figure c, there is a one-to-many relationship between customers and customer employees. Because a customer has many employees but an employee, a person, works in only one store.

But I don't think so, for example, the employee number 30441 works for both customer number 0121 and 2198, and likewise, one customer number not only works for one employee. So I think it's a many-to-many relationship between customers and customer employees.

What's more, here are the example and explanation that the textbook provides as the many-to-many relationship between Salesperson number and Product Number.

It said each salesperson can sell any or all of products and each product can be sold by any or all of its salesperson.

But I think there is the same relationship as upper one, the product number 21765 is sold by not only one salesperson(186 and 361), and the Salesperson number 137 sales 3 different product(19440, 24013, 26722).

Could you point out the point that makes me so confused? I don't get the difference between one-to-many and many-to-many relationships as the textbook explained.

Explanation / Answer

In the CUSTOMER EMPLOYEE relation table:
In the one-to-many relationship,
Here one customer is mapped to multiple Employees.

Eg: For customer number 2198 it is mapped to employee numbers 27470, 30441, 33779, 35268 means one customer number is mapped to multiple employee numbers.

In this scenario Many-to-Many relationship means many customers to be mapped many employees. Like customer number 2198 it is mapped to employee numbers 27470, 30441, 33779, 35268 and vice versa i.e., customer number 0121, 0933, 2198 are mapped multiple employee numbers. But in this case it was'nt like that.

One simple real time example is one cart can add many items.

In the second example SALES relation table
here also the similar relationship is applied.
Yes, you are right it a vice versa. It depends on which side of the relationship the entity is present on.
Here both relationships are similar.

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.