Two links (book sales and cashier) Book sales are the links between books and customers. The cashier's situation is between the cashier and the book.

Attribute number, title, publisher, publication date, author and unit price of the book.

Cashier attribute number, name, gender, etc.

The attributes of book sales: sales time and sales quantity.

Cashier status attributes include cashier time and amount).

If you don't want a customer entity, put the two together.

The attribute is (sales time and sales quantity and amount).