13 How to classify papers In recent years, papers have to submit classification numbers. Some readers are not clear about the classification of papers and it is difficult to classify their own papers. In order to help you classify papers accurately, be familiar with the classification of books and periodicals, and help you retrieve documents, we introduced the knowledge about classification numbers. A classification grade labeling system classifies books according to their subject attributes or other characteristics and gives them corresponding symbols. Its symbol is a combination of Latin letters and numbers. The numbering system adopts "layer-by-layer marking system", also known as grade marking system. Let's take advanced mathematics as an example to understand the numbering method and the layering and hierarchy of book content. Example: Grade One, Mathematical Chemistry, Grade Two, O 1 Mathematics, Grade Three, O 13. It is not difficult to see that grade one is a number, and grade two is two numbers ... that is, "O 1" is the subordinate of "O" and "O/kloc-0" The finer the classification, the longer the class number. Books are very professional and finely divided, and sometimes they can be divided into seven or eight grades or even higher. Compared with books, periodicals are roughly divided, because periodical papers will involve or refer to the contents of related disciplines and cross-disciplines, so periodical papers can be divided into three or four levels after finding their first-class categories. For example, the first category of power system automation is "T" industrial technology, the second category is "TM" electrical technology, the third category is "TM7" power grid and power system, and the fourth category is "TM76" power system automation classification number. According to the subject nature of documents, the two classifications classify the contents of documents into the most appropriate categories in the classification system. After determining the main content and theme attributes of the document, we can find the appropriate category in the classification and classify the document into this category. At the same time, you can also use the index of the classification used as a reference to find the corresponding category and compare it with the main table and index. You can also classify it as should be included. The following two points should be noted when classifying: 1) First, determine the category to which the document belongs, and then carefully check the basic categories under the category step by step until you find the most suitable category. For example, "metal material" appears as a category in "TG metallurgy, metal technology" and "earth architecture science", but the meaning of the category is quite different. TG 14 metal TU5 1 metal material14/black material 51black material 146 non-ferrous metals and their alloys 5 12 non-ferrous and rare metals and their alloys 2. From the classification depth, it is relative, not absolute. That is, the most suitable is not necessarily the lowest stratum, but should be classified according to the provisions of the norms. If a database stipulates that the category of "U Transportation" is only used in the third category, then it is not appropriate to use U66 in the category of "U66 Ship Engineering" for ship refrigeration and air conditioning equipment, and it should be classified as U664.8 and dedicated to this category. At the same time, you can also use the index of the classification used as a reference to find the corresponding category and compare it with the main table and index. You can also classify it as should be included. The following two points should be noted when classifying: 1) First, determine the category to which the document belongs, and then carefully check the basic categories under the category step by step until you find the most suitable category.