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Patents: Patent Classification Searching

Patent Classification Searching

Depending on the database and the age of the patent, often there are few, if any, keyword fields (title, abstracts, indexing). For example, U.S. patent records in the USPTO database prior to 1976 can only be retrieved by issue date, patent classification codes, and patent number. Hence, to do the most comprehensive search possible, one must identify classification codes for the topic of interest. However, a searcher faces three major challenges:

  1. Classification systems are very detailed and extensively hierarchical.
  2. Given the level of detail, multiple classification codes are usually assigned to a patent, each designating a particular aspect of the invention. Hence, the full invention is often described only by a combination of codes.
  3. Historically, there were three major classification systems: U.S., ECLA (European Patent Office), and International Patent (IPC) systems.  Fortunately, a new system, the Cooperative Patent Classification (CPC) system has recently been developed. As of early 2015, patents from at least 18 countries have been assigned CPC codes in ESPACENET.  This includes U.S. patents back to July, 1836, many European countries, China, World (PCT), and Japan. It is expected that eventually nearly all patent offices will adopt the CPC system. The ECLA system has been completely replaced by the CPC already.

 The good news is that all the classifications systems have an easily searchable/browsable free online database.

Whenever possible, it is recommended that CPC codes be searched. The CPC is much more up-to-date and detailed compared to the other two systems. Often the best strategy is to retrieve patents with a good keyword search and then examination the description of the classification codes assigned to the most relevant patents.  Finally, do a second search using some combination of the most relevant codes.  

For more information about the CPC system, see CPC FAQs and CPC About Information.

Engineering Librarian

Erin Rowley's picture
Erin Rowley
108A Lockwood Library
University at Buffalo
Buffalo, NY 14260

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