After the retrospective database is completed, every book in the library has its own identity, and the computer can identify the book by recording its barcode number. Retrospective database building is a necessary work in the early stage of library automation management, and all later work will be carried out on this basis. Therefore, retrospective database building is the basis of the whole automatic management, which is very important, and there can be no mistakes, otherwise it will affect the later circulation and borrowing links. The purpose of retrospective database construction is to establish computer-readable information for each book in the system through cataloging and collecting books. In the future, computers will establish contact with readers' barcodes by reading them, so as to record the circulation of books and provide readers with various ways to find books. The ultimate goal is to reduce the workload of library teachers, better provide high-quality and efficient services for readers and promote teaching and scientific research. When a book is put on the shelf, a label will be attached to the spine of the book. Generally, we call it book label for short, which will write the classification number of books and the distinguishing number of similar books. The classification number and the distinguishing number of similar books are used as the basis for book shelving and readers to find books. Therefore, the classification number and distinguishing number of similar books together are called shelving number or call number (call number). Therefore, the call number is not only the classification number, because books with the same classification number need to be distinguished by more marks, so the call number is the sum of the classification number and the classification number of similar books. Call number can also be called shelving number, which indicates the shelving position of documents in the collection for extraction and shelving. The books in the library are arranged according to the call numbers. Generally composed of letters, numbers and other symbols. The distinguishing number of similar books generally consists of book number and additional number, and book number is the number used to mainly express the difference between similar books. In the library industry, the most commonly used book numbering methods are species number and author number, but a library can only choose one method. Classification number refers to books with the same classification number, and they are numbered according to the order in which the books arrive in the library. For example, the library has the following books, A Dream of Red Mansions, Romance of the Three Kingdoms and Water Margin, which have entered the library cataloguing work in turn. Then, if these three books are classified according to the China Library Classification (4th edition), the classification numbers are all I242.2 (such numbers represent classic chapters). These books will be numbered 1, 2 and 3 respectively (assuming that these three books are the first time to enter the library), and their call numbers (shelving numbers) are I242.2/ 1, I242.2/2 and I242.2/3. The author number distinguishes similar books according to the author, not according to the order of entering the library. According to the different characteristics of authors, it can be divided into four-corner numbering method, China general author number table, pinyin method and other mixed methods. These methods all need to look up the corresponding table or decode the text, and the methods are complicated. The classification number (author number) of CSLN "Network Map" library system is automatically generated according to the classification number. If you have made a book with the classification number G623.2 in your library (the classification number is 00 1), when you make another book, the classification number will automatically generate 002, forming the call number G623.2/002. Note: The classification number of marc data of China Professional Library Network is classified according to China Library Classification, and there are 22 categories. The classification number can be found in the CIP of this book. Generally speaking, there are reference classification numbers in CIP data of officially published books. CIP style: Notes International Standard Book Number (1SBN) I. Title II. Author III. Keyword four. Other descriptions of classification number IV is the reference classification number of this book.