The book only has ISBN number, and now it is composed of 13 digits, and 978 and 979 are European commodity codes. In addition, the publication of standards and specifications in China generally adopts the uniform book number. These are the two numbers that can appear in the book. In library retrieval, besides the above two numbers, there are also classification numbers and call numbers. It is necessary to use subject words and keywords in library retrieval. Because the shelving of the library basically adopts the method of classified shelving, when you find a related book, you can browse back and forth (open the shelf) to find all kinds of books of the same kind, and perhaps the most suitable book is here.