In the basic category list of China Library Classification, category R stands for medical and health category. In the category of periodical classification table of Henan University Library, category R stands for physics and its application.

Categories will also be divided into first-class categories and second-class categories, and some will be extended to fifth or even sixth-class categories. For example, clothing is a first-class category, divided into men's wear, women's wear and children's wear, which can be defined as a second-class category. The next category is the detailed definition and division of men's and women's clothes.

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The operation of sketch class should focus on highlighting functions. Compared with the big category, the small category has concentrated and accurate flow. Because he can only search by fixed keywords. Therefore, merchants can pay attention to planning and strengthen the scene effect after the goods are used when making the sketch master map.

However, some categories have the characteristics of both large and small categories. If merchants encounter such a category, they should combine the above two methods to operate. Pay attention to both style and planning.