As an English-speaking patent searcher, sure, you feel comfortable looking up US and IPC classification codes. The classification schedules are easy enough to browse, and you probably understand the hierarchical organization of the systems pretty well. But what about Japanese patent searching – can you use the Japanese national patent classification system with the same confidence ?
Japan is an important source in patent searching – it is well known in the IP industry that the Japanese patent office produces a high volume of patent literature and that this collection is rich in important technical innovations. As one of the Trilateral offices, the JPO has worked on initiatives to make its collection more accessible to non-Japanese speakers, including the introduction of the Patent Abstracts of Japan file, the major source of English abstracts for Japanese patent applications.
However, to more effectively search their own collection, the Japanese patent office developed two in-house classification systems, known as Japanese File Index terms and Japanese F-terms, respectively. To effectively search the Japanese collection in-depth, it’s a good idea to get acquainted with these two systems. Fortunately, these two class schedules are available (at least in part) in English. When used in concert, they can provide a powerful method for effective Japanese patent searching.
While these two classification systems are often treated together, they are quite different. File Index (also called F-Index or FI) terms were created to be an extension of the International Patent Classification (IPC). For an example of how the FI terms extend the IPC classification codes, see the File Index section of the Intellogist glossary article on this topic.
F-terms are used to break down subject areas by technical application. From the JPO website:
F-terms re-classify or further segment each specific technical field of IPC from a variety of viewpoints (i.e., objective, application, structure, material, manufacturing process, processing and operation method, control method, etc.). Combining F-terms with IPC effectively narrows down relevant documents in prior art search.
While FI codes are structurally similar to IPC codes, F-terms have a multidimensional, faceted structure that may be unfamiliar to some patent searchers. F-terms are often much narrower in scope than IPC or FI terms. In a 2008 article on the subject, Stephen Adams stated that Paterra had calculated an average of 14 F-terms per document, and that some individual documents were known to bear more than 50 terms. Adams suggests that because F-terms specifically seek to classify the technology used in the invention, these codes may be especially useful for locating known technologies used in unsuspected or cross-disciplinary applications. 
For a comparison of related IPC, ECLA, File Index (FI), and F-term classification areas, you can browse the classification definitions provided in the Intellogist article on Japanese File Index and F-terms.
Although they offer many advantages, F-terms were wholly electronic (not published on patent faces) for quite some time, which means that the backfile data must be obtained by providers from the IPDL. Notably, many search systems have not added the classifications to the full backfile of JP patent documents (thus, the start date for coverage may differ between systems). Questel (QPAT, Qweb) is one exception, and can offer complete F-term coverage due to their historical relationship with the Patolis corporation.
1. Adams (2008). “English-language support tools for the use of Japanese F-term patent subject searching online.” World Patent Information, vol. 30(1): pages 5-20.
This post was edited by Intellogist Team member Kristin Whitman. The Intellogist blog is provided for free by Intellogist’s parent company, Landon IP, a major provider of patent search, technical translation, and information services.