According to China Library Classification, referred to as Chinese Library Classification, and according to China Library Classification, all disciplines are divided into 5 departments and 22 categories. Books are shelved according to the call number, which is the classification number+category number of China Library Classification, which is convenient for readers to query books.

This classification should be studied systematically.

After the books in the library are classified according to the classification adopted, the purpose of "gathering books together" is achieved. However, in the same kind of books, there are many books with different titles, different authors, different translators and different versions. For example, the classification number of Introduction to English Phonetics is H3 1 1, and that of Practical English Phonetics is H3 1 1. Therefore, just classifying and numbering books can't meet every completely personalized requirement. In order to facilitate the management and utilization of books, it is necessary to further distinguish similar books. This requires an auxiliary method to give a specific number on the basis of book classification, which is called "book number". Therefore, the book number of each book is composed of "classification number" and "book number", which is called "call number" for borrowers and "shelf number" for books.

The library uses the "species number" as the "book number", that is, according to the order of classification and cataloging of similar books, each book is given a number. For example: H3111,H31/2, ... H3113, etc. , and the number after "/"is "species number".