1. There are labels on the spine of books in general libraries. There are two sets of numbers on the label, one is the classification number and the other is the book number.

2. The call number consists of two groups of numbers: the classification number and the book number. The classification number represents the nature of the subject to which the document content belongs, which arranges similar books together, and the book number represents the classification number of similar documents, which determines the arrangement order of similar books.

These books are arranged in the order of claim number. According to the alphabetical order of classification numbers, those with the same letters are sorted by the first number after the letters, and those with the same letters and the first number are sorted by the second number.