About Patent Classification

Patent classification schemes are used to organize and index the technical content of patent specifications so that specifications on a specific topic or in a given area of technology can be identified easily and accurately. This page explains in detail how to use it and should ideally be used together with our Patent Search page.
Patent classification schemes are constructed and maintained by and for patent examiners and their primary purpose is to help the examiners in their work. When examining a patent application, the examiner needs to search a collection of patent documents to identify relevant existing patent specifications and this task is facilitated by the use of a tailor-made classification scheme.
As part of the examination process an examiner will assign patent classification codes to the specification he is examining, so in its turn that specification becomes part of the classified collection of specifications available to examiners in the future. Therefore the classified collection of patent documents is growing constantly.
The usefulness of patent classification as a means of searching for patents information is a by-product of its primary purpose as a tool for patent examiners. Using patent classification as part of a search to identify patents in a particular field can help the non-expert searcher to focus and refine his search and produce a useful set of references.

The International Patent Classification
The International Patent Classification (IPC) is currently used by over 70 patent authorities to classify and index the subject matter of published patent specifications. The IPC is maintained and is administered by the World Intellectual Property Organization and was first published in 1968. The eighth edition was published in mid 2005 and came into force in January 2006.
The IPC is available on online as well as in hard copy. Note that the current eighth edition's hard copy version is only an abridged "Core" version.

Structure
The IPC divides patentable technology into 8 key areas:
A: Human Necessities
B: Performing Operations, Transporting
C: Chemistry, Metallurgy
D: Textiles, Paper
E: Fixed Constructions
F: Mechanical Engineering, Lighting, Heating, Weapons
G: Physics
H: Electricity
Within these areas technology is divided and subdivided to a detailed level, which allows the subject matter of a patent specification to be very thoroughly classified.
Each of the areas A to H is published as a separate volume and together they are referred to as the schedules. The schedules are accompanied by the following volumes:
The Guide - which contains much useful information and advice on how the scheme should be used
Concordance - which identifies areas in the current edition which have been revised since the publication of the preceding edition.
The Catchword Index - which is a basic key word index identifying the area of the IPC schedules where specifications on a given topic are likely to be classified
The IPC codes, which act as an index to the subject matter of the patent, are printed on the front page of a patent specification and are always identified by the INID code 51. There is usually a superscript numeral indicating which edition of the IPC has been used to classify the document. e.g.
The 8th edition of the International Patent Classification has meant many changes. The IPC has always been hindered by new and revised classes every 5 years since the 1st edition in 1968, so that you often have to check back through the editions for the equivalent (or as close as you can get) class in earlier editions.
A single classification code can now be used going back not just to 1968 but often earlier. There were other changes. There is Core, a simple version which will be revised every 3 years, and Advanced, which will be revised every 3 months. For those familiar with the IPC, Advanced looks like the old IPC. Core cannot be easily distinguished from it: it lacks many of the subclasses such as 25/02, 25/04 (but does retain some). Those who wish to search for appropriate Core classes can select the Core level on the Web classification, which otherwise defaults to Advanced. It is to be hoped that future classification changes introduced to the Web version will be well publicized as otherwise there will be constant checking to see if a class long-used by the researcher has been altered.
Besides Core and Advanced, there will be a distinction in each area for Invention and Non Invention (the latter were formerly called Indexing classes). Non Invention is for interesting but not novel aspects of the invention. An invention involving thermosetting materials may be meant for tights, in which case an appropriate class can be added (tubular garments).

Using the International Patent Classification
Since the IPC is used by virtually all of the active patenting authorities in the world (and particularly by all the authorities of the major industrialized nations) as a common means of classifying the patent specifications they publish, it is possible to carry out an international search for patents on a specific subject using the IPC as a key. However, it is a massive and complex tool designed for an expert user group and when it is used by anyone outside that user group it should be applied with care.

Finding the "right" IPC classification code
Finding a classification code (or codes) upon which to base a search requires a basic grasp of how the IPC works. Taking time to browse through the Guide may help, but talking to someone who is familiar with using the IPC as a search tool will be of most value.
A surprising range (or scatter) of classification codes at different levels of detail and even from different areas of the IPC can be assigned to specifications forming part of a single patent family and describing the same invention, or to specifications which are closely related in terms of their technical content. There are a number of factors which contribute to this IPC scatter:
The classification policy of individual examining authorities may vary. Local practice may place emphasis on different features of the invention.
The interpretation and subsequent classification of specifications on the same topic may vary from examiner to examiner.
In the various language editions of the IPC terms may not have exactly the same significance and this can lead to some scatter in assigning IPC marks.
Patent equivalents, though all describing the same invention, will not necessarily be expressed in the same way or stress the same points: a particular application of an invention may be stressed in a European specification while another application may be stressed in its Canadian equivalent.
Some patent offices only apply the IPC at a very general level.
The USPTO assigns IPC codes to its specifications via an automated concordance which is often "off target".
In short, the scatter means that it is important not to fix upon a single, very specific IPC code and to base all subsequent subject searching on that single code alone. Even if it is possible to identify an IPC classification code which appears to express perfectly the subject to be searched, it is essential to consult the full IPC schedules, to look at the hierachical context in which the code exists, to read the notes, to consider searching using a less specific code and to consider alternative codes. Note that the heirarchy is indicated on the schedules by the number of dots and that for example a 4 dot code must be read in conjunction with the 3, 2 and 1 dot group titles immediately above.