The book number usually referred to the book's ismn or author's ismn was a book number used to distinguish between different publishing houses or authors. The function of the book number was as follows: 1. Identification of the source of the book: Books from different publishing houses or authors have different ISBN-numbers, which can be used to accurately identify the source of the book. 2. To facilitate book sales and statistics: In the process of book sales, the book number can help the seller distinguish the books of different publishing houses or authors and facilitate statistics. 3. Protect the author's rights and interests: The book number allows the author to have a unique identification of his book to protect the author's rights and interests. 4. It is convenient for library management: the book number can conveniently count, inquire and manage books, which is convenient for the library to classify and collect books. Book numbers were of great significance to the sale, management, and collection of books.