1. A book's ID card refers to its Chinese standard book number. The first part of this numbering system is the International Standard Book Number (ISBN), which can be used independently. It consists of 10 digits, separated by a hyphen "-",and is divided into four parts, which respectively represent the group number, publisher number, book number and parity bit. The lengths of the other three segments are variable, except that the parity bit is fixed at one bit, but the sum of the digits of these three segments must be nine bits, and a parity bit is added, so that the digits of the serial number length 1SBN are always equal to 10. When the parity bit is 10, it is represented by the capital letter "X", and when the parity bit is 1 1, it is represented by "O".

2. The ID card of the periodical is CN. CN stands for China Uniform Serial Number. Regular periodicals must have a unified serial number in China, namely the CN number. The CN mentioned here generally refers to Chinese mainland, Hong Kong, Macao and Taiwan. All regular periodicals must have a CN number. The General Administration of Press and Publication will examine the applicants of a periodical, and if they meet the requirements, they will approve a serial number, that is, the CN number. The CN number here is actually the ID number of the journal.

3. The ID card of Chinese and English papers is DOI number. The principle of DOI is that when a paper is published by a publishing house, the international DOI foundation (IDF for short) is responsible for providing a unique and permanent DOI, regardless of the specific location where digital resources are stored. In the coding scheme of DOI, there is no limit to the character length of prefix and suffix, so the capacity of the coding system of DOI is infinite. The prefix is determined by IDF and the suffix is specified by the publisher of digital resources to ensure the uniqueness of any digital materials.