Library card (library card number, name, gender, work unit)

Books (book number, category, title, author, publishing house, publication date, pricing)

Borrowing books (reader number, book number, borrowing date, expiration date, quantity)

Underline:

Library card number

book number

Reader number, book number

Note: Not all the attributes are marked on the map. Please add it yourself. It is enough to add a quantity to the relationship attribute, and the others are simple.