File Index (FI) classification: another JPO classification system
There are 3 classification systems for Japanese patents: F-term, File Index (FI), and IPC. Most professional searchers consider FI search a more precise system than IPC.
File Index (FI) classification:
FI or "File Index" is the internal classification system used by the Japanese Patent Office to classify technical contents of patent documents and to organise prior-art searches more efficiently.
FI classifications are made up of an International Patent Classification (IPC) sub-group, followed by an IPC subdivision symbol in the form of a three-digit number. These IPC subdivision symbols are unique to FI classes and are structured hierarchically. Optionally, a file discrimination symbol in the form of a letter can be added.
With its various subdivisions, the File Index (FI) classification has about 170 000 classes, whereas the IPC has some 70 000 only. FI is a more precise and thorough jp patent search than IPC. We often use combination of FI and key word strings.