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What is a citation?

Citations are documents that are linked together when one document mentions another as having related content. In the world outside of patent literature, “citation” is a also a commonly used term for a bibliographic extract of a journal article or other similar scholarly work—in other words, the term “citation” can be used interchangeably with the term “record.” However, for the purposes of the articles here, we have made an attempt to refer to these extracts as “records” to avoid confusion with the more specific patent related definition of “citation.”

There are two reasons why a patent can be cited by another patent: the applicant disclosed it as known prior art, or the examiner found it during the search. For example, say patent A was issued in 1993 for a beanie with a simple propeller, and patent B was issued in 2003 for a beanie with a motorized propeller. The first scenario is that the inventor was aware of earlier beanie hat patents, so when he filed his application he was required by law to disclose these known patents, including patent A. The second scenario is that the inventor had no knowledge of earlier beanie hat patents, but the Examiner found Patent A as relevant art during the search (though it was not relevant enough to use for a total rejection).

What is a backward or forward citation?

When two documents are linked together in this way, both can be alternately referred to as the "citation" depending one's point of view. The terms used to clarify the relationship are "backward citation" and "forward citation." A "backward citation" is the term used for a traditional citation: it is the document that was published earlier, and which appears on the newer document’s front page. In turn, the newer document is called the "forward citation" or "citing document."

If Patent A (1993) is cited by Patent B (2003)
Patent A is a backward citation of Patent B
Patent B is a forward citation of Patent A

Obviously, forward citations cannot appear on a document’s front page, since no one can see the future, and patents are published at time of issue. However, forward citations can easily appear on the patent record in an electronic database, and most search databases allow both backward and forward citation searching.

Why should I search using citations?

Citation relationships are created when two documents are found to have related content. Therefore, citation searching is an excellent way to discover other patents closely related to an interesting document. Unless there are special circumstances, a forward and backward citation search should be performed on each highly relevant document uncovered by a keyword or class search.

One important benefit of a citation search is that it can expose a new relevant document not found during the initial class or keyword search. Such a document might be classified in a different area, or contain different keywords than the ones used in the initial search. These clues might be used to broaden or re-formulate the search strategy.

What is a relevancy indicator?

Relevancy indicators are applied to citations found by Examiners, to give an idea of the citation’s content. When Examiners perform a search to investigate the patentability of an application, they typically find many related references. Some of these documents might be useful to the Examiner in making a partial rejection of the claims, while other documents merely contain a good background of the technical field and advances up to this point. Examiners are encouraged to cite this background material, as well as the more on-target references, as a courtesy to any searchers who come across the patent and wish to learn more. To clarify which type of reference each citation is, examiners apply three major codes to their citations: X, Y, and A. An X document is used to reject one or more claims on its own, a Y document is used to reject a claim in combination with another reference (using an obviousness argument), and an A document is a document with related technical material.

In certain cases, especially for European (EP) and PCT (WO) documents, search services are able to obtain and include relevancy indicators along with the citations they display. These codes helps searchers choose what documents might be most closely related to the document subject matter (X documents), and what documents are likely to give background information only (A documents). Thus, relevancy indicators can help users search citations more efficiently. Not every search engine includes relevancy indicators with its citation data, however.

Who produces citation data?

Patent offices may produce their own electronic records that include citation data. However, the European Patent Office (EPO) is probably the main source for most search databases. The EPO collects, produces and maintains patent bibliographic data (including citation data) for major patenting authorities from around the world.

Until May 2007, citation data was produced by the EPO in a data file called "REFI." The REFI product was discontinued upon the release of the new, improved INPADOC/DOCDB bibliographic database in May 2007, and DOCDB became the all-inclusive bibliographic data product distributed by the EPO.

What obstacles exist when searching citation data in online services?

Although any fee-based search service should offer a citation search feature, some of them are more efficient than others. Some search engines simply place hyperlinked patent numbers in the bibliographic information, while others allow users to create a new hit list out of citations on a document to review them in-depth. Some services even produce graphical representations of citation relationships over multiple generations.

There are also different interpretations among these services about how a citation search should be performed. At least one search service, Questel-Orbit QPAT, performs a citation search not only on a subject patent, but also on every other member of its patent family in parallel, creating a much larger results set because it is drawing in citations from equivalent patents published in other countries.

Because of these differences, users should be aware of how a service is searching citations, and what data it covers, in order to ensure the search is complete and accurate.

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