Suppose a large library needs to design a book management system, which needs to have the following functions: (1) Borrowing books: Enter the reader's library card. First, the system checks whether the library card is valid. If it is valid, create a file on the library card for readers who borrow books for the first time. Otherwise, refer to the borrowing documents to see if the readers have borrowed more than 20 books. Refuse to borrow if it has reached 20 books, and borrow if it has not reached 20 books (check the inventory, modify the inventory directory, and enter the reader's book borrowing situation into the book borrowing list. (2) Book return: read the records related to readers from the borrowing documents, check the borrowing date, and be fined for overdue (1 month). Otherwise, modify the inventory directory and borrowing documents. ⑶ Inquiry: Inquire about readers, book borrowing and inventory through borrowing documents and inventory catalogue documents, and print statistical tables. The requirements are as follows: 1 one copy of demand analysis and overall design scheme; ② Illustrated with pictures and texts; 3. Documents prepared according to given standards and examples; 4 covers; 5 automatically generated directories; On this basis, it can be expanded and supplemented appropriately.