In this discussion I will cover searching patents and applications at the USPTO web site. Much of what I will discuss is also applicable to other web sites, such as esp@cenet.
There are two main ways of searching patents for novelty:
You perform a keyword search by entering keywords, words that you think describe the invention, and logical operators (and, or, andnot) that describe the relationships between the keywords. For example, go to the advanced search page of the USPTO web site. To find patents related to cat doors, the little door within a door that a cat can use to go in and out, you would enter a query like the following:
spec/cat and (flap or door)
This query searches the specifications of US Patents from 1976 to present and it retrieves 1355 answers (August 20, 2004), many of which appear off target. To narrow the results we can search just the abstracts, or just the titles of patents. Let's search the abstracts
abst/cat and (flap or door)
Searching the abstracts retrieves 118 patents, most of which seem to be relevant to cats and doors. Browsing the list we can see that patent number 4,991,350 seems particularly relevant.
Now that we've found one relevant reference we can use it to help us to find other useful references. First, look at the current US Classification. The main class is listed as 49/169. This code can be used later in a classification search. Next look at the references cited. In this case there are five patents cited, starting with 4,022,263. These are the references cited by the applicant or the examiner during the prosecution of the patent. There could be gold here. Click on the hyperlinks and read these patents, or at least read the front page. Finally, take a look at "referenced by" which is located to the right of "references cited". Click on the hyperlink. These are the subsequent patents that referenced the patent we are viewing. Again these patents may be highly useful. They are worth reading carefully.
After examining the cited, and citing references it is time to perform a classification search. Entering
ccl/49/169
retrieves 49 references based upon the U.S. patent classification code. Now browse the references and take a look at the classifications, the cited, and the citing references. Read the patents. Look for other useful keywords and classification codes, then re-search using the new keywords and classification codes. Searching is an iterative process.
The eternal question of patent searching is: When do I stop searching? It depends. A search for patents to invalidate an existing patent will need to be much more thorough than a search to establish novelty. A good rule of thumb to stop is when you keep finding the same patents over and over again while using different search queries. You are probably hitting the point of diminishing returns. Other points to keep in mind are:
Happy searching