according to the technical subject, USPC arranges all American patent documents and other technical documents belonging to the technical subject, forming a certain number of document collections. There are big categories and small categories in USPC, each of which describes different technical topics, while the small category describes the technological process, structural characteristics and functional characteristics of the technical topics contained in the big category. The combination of "big class/small class" becomes a complete classification number.
IPC international classification includes five parts: major categories, minor categories and major groups.