The book retrieval number, that is, the call number, is the number given to each book in the library, which has a certain structure and specific significance. In the book collection system, each call number is unique, which can accurately determine the arrangement position of the collected books on the shelf and is very necessary code information for readers to find books.

The book retrieval number consists of two parts: classification number and species number, which are separated by "/". The classification number is the subject attribute identification of books, and the category number is the compilation sequence number of such books.