The USPTO outlines a 7-step U.S. patent search strategy. Listed below are the 7 steps copied verbatim from the USPTO website located here. This webpage and the information below was last accessed in January 2014.
“Classification
1. Brainstorm keywords related to the purpose, and composition of the invention.
2. Look up the words in the Index to the U.S. Patent Classification to find potential class/subclasses.
3. Verify the relevancy of the class/subclasses by using the Classification Schedule in the Manual of Classification.
4. Read the Classification Definitions to verify the scope of the subclasses and note "see also" references.
Access Full-Text
5. Search the Issued Patents and the Published Applications databases by "Current US Classification" and access full-text patents and published applications.
Review and References
6. Review the claims, specifications, and drawings of documents retrieved for relevancy.
7. Check all reference and note the "U.S. Cl." and "Field of Searc" areas for additional class/subclasses to search.”
The USPTO provides a general overview of the classification system here. In general there are nearly 500 different classes identified by by the USPTO (Source: Bobick, J.E., & Berard, G.L. (2011, p.113). Science and technology resources: A guide for information professionals and researchers. Santa Barbara, CA: ABC-CLIO).
To retrieve the best results, it is best to perform both a keyword search and a classification search no matter which database search engine you use (Bobick & Berard, 2011, p. 114). As the USPTO website recommends in one of its 7 steps, it is best to brainstorm a list of potential keywords before conducting a search. Start by examining what the most relevant results are classified as, which may give you an idea of what you are searching for is classified as. For example, you might be interested in finding information about devices that allow for animals to remain still while being treated like a veterinarian. However, one problem is that you do not know the name of the device(s) nor do you know the name of any inventor.
To begin your search, you may want to examine the index to the United States Patent Classification (USPC) System on the USPTO website. One possible term that you would check would be "animal," which is 428/16. Looking at the terms under "animal," one relevant term may be "taming or training devices." Clicking on that link will show you the classification number and sub-classification number 119/712+ for "taming or training devices." The sub-classification numbers 712+ show a number of patents listed under "Animal Controlling or Handling." At this point it is probably best to search under classification number 119/756. Under this heading, you will find "Having Animal Positioning Restraint." Clicking on the red "P" icon will show you a list of patents under this heading. The first result is "Animal Restraint Device." This is probably one of a number of relevant results. Clicking on the patent name will show you the entire patent.
