First of all, from the definition of IPC, we can see that IPC category labels are multi-level, and the depth of each level reaches five levels. Secondly, from the classification principle of IPC, according to different classification principles, a patent often has multiple tags, and most patents retrieved from USPTO official website have multiple IPC tags. For example, the IPC number of U.S. Patent No.49 10036 is A23L I/0522；; ; A23L 1/32 1 A23L 1/39 1 A23L 00 1/32 1A23L 00 1/ 195； A2 1D 002/36. There are also many IPC labels provided by Japanese patents. The main reason for multi-IPC tags is that there is overlap between the classification principles of IPC category system. Some patents will have a corresponding IPC according to the functional classification, and a corresponding different TPC mark according to the application classification.
For example, a camera capable of loading a plurality of films and exposing the films prepared therein as required and its device on an airplane. That is, classified by function G03B 1 9/06 and classified by application B64D47/08.