A Patent Search Strategy: Keyword Semantics and Classification Searching

Ran Raider, Government and Legal Information Coordinator, Wright State University Libraries, Patent and Trademark Resource Center, Dayton, OH

One of the Patent and Trademark Resource Centers roles is to educate and instruct the independent inventor on how to perform a preliminary patent document search. The USPTO recommends using their “7 Step Method” guide in instructing independent inventors in performing a preliminary patent search. Even those independent inventors who have advanced degrees in engineering or a science have a difficult time in performing patent document searches. These “hard cases” tend to dwell on their own semantics and bias in beginning their patent document searches. This paper is designed to give the independent inventor, and those that help them, a point of departure in performing a preliminary patent search based on keywords and classifications. The focus of this paper is on patent document searches.

The patent search is used to validate a potential invention. Most beginning inventors wrongly assume that since they have never seen it before, it is therefore, an original and unique invention. This assumption is usually based on their own experience, shopping habits, or lack of knowledge of the marketplace. Validating an invention is a long and sometimes frustrating process. It is a process an independent inventor cannot avoid unless they hire a professional patent searcher to perform the search. That option is most likely beyond the independent inventor’s wherewithal since patent searchers can charge $1000 to $2400 to perform a search . An independent inventor, with patience, can save themselves money by lessening the billable hours attorneys and patent searchers charge. A patent literature search is a discovery process that enables the independent inventor to validate their idea.

All it takes is one public disclosure to kill an invention’s claim in a patent application. The disclosure can include applications and issued patents or any public domain document, for example, an article from a popular magazine such as Mad Magazine. Independent inventors usually just search patents and nothing else. When an independent inventor does a search, it is considered merely a preliminary patent search. The limitations of their search must be stressed to the independent inventor. With so many patent documents to search there is always the possibility of missing an important piece both in the patent documents and in the public disclosures. This is why a final search should always be conducted by a patent professional before the submission of a patent application.

Before beginning a patent search an independent inventor needs to understand the concept of “prior art.” Prior art is also known as “state of the art” and constitutes all prior information on a particular technology or science. This information can take any form as long as it is available to the public before the patent application is submitted. Typically, but not limited to, prior art constitutes patent applications and grants, magazine or journal articles, catalogs, web sites, trade shows and books. Prior art comprises all the information that is relevant to the invention, appearance, how it is made, what processes it uses, composition of matter and function. The purpose of a prior art search is not to find the exact invention but rather similar technologies and science as they compare to the invention. This comparison substantiates the claimed invention as novel/new, useful and non-obvious versus the prior art. When an inventor searches the patent documents they are performing a preliminary prior art search. This prior art search helps in the decision making as to whether to proceed with their application for patent protection. This prior art search is also used in their discussion with a patent professional. The patent professional will advise whether their invention will survive the examination process based on the claims the inventor is submitting for examination against the prior art they have found. Prior art is used by the patent professional to establish the boundaries of the claims of invention.

For the independent inventor, researching their own invention can seem daunting. When an independent inventor encounters problems with their search frustration can easily take hold of them. Breaking the process down into several steps helps the inventor organize not only their thoughts but also where, what and how they will conduct their search. So how does one go about “looking” for their idea in all the patent documents? The idea or invention needs to be broken down into key concepts/components, functions, purpose, and industry. Once the proper terms have been established there are two different ways to begin a “patent” search, or more correctly, a “prior art” search.

Documenting the search is critical to avoid duplication of efforts. A bound or glued notebook, similar to a lab notebook, is used to document not only the invention but also the search process. This inventor’s notebook will help organize the inventor’s thoughts and efforts during the preliminary prior art search.

The first way most inventors begin their search is by using a few keywords. This usual means that the inventor goes to one of the free patent databases and just types in what they call their invention. The results will vary but the majority of the time inventors can get thousands of results or worse, none at all. This overwhelming number tends to slow the search for relevant patent documents just by the sheer number of documents the inventor has to view. Most of the patent documents found using a keyword search will be irrelevant to their invention.

Another issue with keyword based searches is that the inventor’s semantics or spelling may not match the terminology of another inventor or their patent professional. The English language can be used in an attempt to hide patents from searchers. Everyone drafting a patent application is allowed to create their own terminology to describe their invention as long as the patent examiners understand the key concepts of the invention. A new meaning of a word can be ascribed to a function of an invention. For example, a “mouse trap” can also be a “rodent extermination device.” One word, such as dog, can have many meanings: the canine variety; the dog in a ratchet; and the carpenter’s dog that holds down wood on a workbench. Another problem with keyword searching is that 55% of all US applications are from foreign entities. Those foreign entity applications may have been poorly translated or the patent documents may contain misspelled words. Foreign applications may use colour instead of color or tyre instead of tire. Another issue, is that very few spelling errors in patent documents are ever corrected because you have to pay a fee to fix the errors. All of these variations of language and grammar make keyword searching unreliable and dangerous to depend on.

The second way rather than using keywords in a search is to use the classification system. But this doesn’t make it any easier for an inventor to do a patent search. There are a variety of classification systems in the world, the United States Patent Classification System (USPC), the former European Patent Classification System (ECLA), the Cooperative Patent Classification System, the International Patent Classification (IPC), and the Japanese classification systems (F-Term and F-Index). Classification systems were devised to help route applications to the pertinent patent examiners and to increase efficiencies in the examining process. The classification systems were designed by examiners to be used in the categorization of science and technology.

So why is classification the preferred way to do a patent search? The classification systems provide a hierarchical structure to technologies and sciences categorizing them according to function, composition, manufacture, and process. A simple example would be the classification for “Land Vehicles” in the USPC. An example of a class is 280, Land Vehicles. Every invention that travels across land, cars, trucks, bicycles, skateboards, wheelchairs, etc. is included in this classification. So a patent search using the classification system allows the inventor to find all the skates in one place, no matter if the inventors or attorney calls it a “small wheeled mobility device” in the application. The “small wheeled mobility device” will be classified in Class 280 as a skate. The classification systems organize patent applications and grants into categories that make those classified applications and grants relevant to each other.

In reality, the inventor needs to conduct a search using both of the above techniques, keyword and classification. A search using just one technique is not enough to do a preliminary patent search. The following examples use the United States Patent and Trademark Office web databases PatFT and AppFT.

Keyword Searching Basics

Just what does a keyword patent search mean? Most inventors use keyword searches to determine if their idea already exists. It is the simplest method to begin a patent search. Coming up with the right words to use is sometimes the biggest problem. For example, I have an invention for an electronic scoring system for a bristle dartboard. A simple patent search using the term dartboard is performed by the inventor. Using the USPTO patent grant database (PatFT), the keyword “dartboard” retrieves approximately 137 patents. But a closer look at those patent documents reveals that a majority of them have nothing to do with dartboards, even though each document in my search contained the word “dartboard.” Why did this happen? The word dartboard can be used in many different contexts. If we look at patent 8,075,137, “Stimulus method for multifocal visual evoked potential” we can see that the word dartboard is used as a related concept comparison between the invention and a “known” object. The word “dartboard” is used in the patent this way: fifty-eight test zones are arranged in a cortically-scaled dartboard configuration in concentric rings. Using a keyword to search for an invention draws out many different meanings and contexts on how a keyword is used.

Was using the term “dartboard” the best place to begin? It is almost counter intuitive that an inventor must understand what they are inventing. Is it a dartboard or a new way of keeping score electronically on a bristle dartboard? They may think that they are inventing a new dartboard and proceed to search using that false concept. The inventor needs to brainstorm keywords that describe:

1. Purpose
2. Proximate/essential function
3. Composition
4. End result

Some other keywords to consider are from the marketplace and related products. For example: the marketplace for dartboards is amusement devices, games, and toys. For related devices the inventor would also consider targets. So using the above method of brainstorming:

1. Purpose: keeping track of projectile (dart) impacts on bristle dartboards or targets and electronically relaying positional impacts to an electronic scoring system
2. Proximate function: projectile (dart) impact generates electronic signal which is received by an electronic score keeping device and displays the results
3. Composition: impact resistant material that is puncture proof and contains a pressure sensitive device
4. End result: conveniently keeps track of scoring for a game of steel tip darts.

Let’s further expand the description of our invention for an electronic scoring system for bristle dartboards. Other keyword concepts include: pressure sensitive, positional, detection and puncture resistant. Part of the process of performing a keyword search is that other appropriate terms and keywords will be found during the search. These new terms will be documented by the independent inventor to expand the search. By expanding the terminology being used, the independent inventor will find relevant patent documents. A goal with the preliminary keyword search is to find relevant patent classifications. During the discovery process, the independent inventors will identify classifications for expanding their search even further.

The USPTO web databases, PatFT and AppFT, allow the inventor to use Boolean operators to connect or include additional words in their searches. There are only two Boolean operators that can be used: AND and OR. You can nest searches between parenthesis: (tire OR tyre). To make two or more terms appear in the same document you can use AND: tire AND tyre. Or a compounded search that uses both Boolean operators: wheel and (tire OR tyre). There is also a variety of other search codes that can be used. The common ones are: ABST/ (abstracts), SPEC/ (specification or description), CCL/ (current US classification), AN/ (assignee or owner’s name), and IN/ (inventor’s name). The use of Boolean operators and search codes in the USPTO patent databases help narrow results to more relevant patent documents. Using these Boolean operators and search codes will increase your chances in finding relevant patent documents.

There are even more factors to consider such as are the terms I am using the only ones that apply to my invention? Technical dictionaries and encyclopedias will help expand terms used in the inventor search. Do I need to expand my search to other devices that may use similar technology? Inventors need to think outside the box when brainstorming for keywords.

Let’s start by using the keywords dart, electronic and board. Note that dartboard will not be used in this preliminary search. The independent inventor will begin their search on the USPTO web site using the PatFT and AppFT patent databases. In both instances, they will use the “Advanced” option in PatFT and AppFT databases. An inventor can narrow down the search by finding the above keywords in the abstract or description/specification of the patent document. The following search string will be used:

abst/dart and abst/electronic and abst/board

A total of 21 patent grants were found.

A reading of those patent documents shows that the classification assigned to dartboards is in class 273, Amusement devices: games. The USPTO further sub-classifies dartboards in the “Aerial projectile game” amusement devices and dartboards specifically in the subordinate subclass defined as “target” (class/subclass: 273/348). Using the class/subclass the inventor can revise their initial search and retrieve a total of 129 issued patents. A search of patent applications by class/subclass retrieves a further 76 documents. A keyword search is used, in this case, as a way to access the classifications assigned to the amusement device, dartboard.

There are major issues with this search strategy. The biggest issue is with the selected classification. The class and subclass 273/348 does return dart boards. And that’s the problem, nothing in these 157 patents address automated scoring systems. The class 273 subclass 348 are about games and methods of games. The class/subclass list of patents includes titles with the words electronic and projectile. But it is missing a major part of the invention: scoring system. Returning to the list of patents retrieved on our keyword search there are several titles that contain the words electronic, dart, scoring, scoreboard and scorekeeping. Looking at those patent documents shows that scoring systems are located in class 340 subclass 323R. In this class and subclass there are 857 patent grants and 49 patent applications. The inventor will need to decide which of these two classes are more pertinent to their invention. They may also decide that neither classes nor subclasses are useful in their search.

Another way to expand a keyword search is by using inventors or assignee names. Inventors tend to invent in the same areas over their careers. While this is not always the case, it is a helpful strategy in a patent search. Assignee, or the company someone works for or sold their invention to, is another strategy that can be used. Sometimes an inventor already knows the names of manufacturers in the industry.

Looking at the patent documents retrieved by using another related class 273/372, two companies are identified as manufactures of electronic dart boards. The following search is performed:

an/arachnid and an/”merit industries”

A total of 48 patent grants are found. Of these 48 patents 13 patent grants are for electronic dart boards and scoring systems.

Limits to Keyword Searches

There is a dangerous limit to keyword searching and that limit is the time period. Full-text keyword searching is limited in the USPTO web databases to after 1975. Only patent documents published after 1975, or in the case of applications, published after March 14, 2001, are available for keyword searching. Another dangerous limit in keyword searches is that few patent databases have a controlled vocabulary. The common phrase “Garbage in Garbage Out” (GIGO) applies to all patent databases, and also to literature/magazine databases. Because words form the weak link in patent searches the only way to overcome the problem is to perform a classification search using one of the national systems, USPC, CPC, IPC or F-Term and F-Index.

This limitation will need to be conveyed to the independent inventor. They must understand that their “research” is merely a preliminary search. Until they use a classification search and view patent documents back to 1790, they have not performed a proper preliminary patent search of US patent documents. They will also need to know that a patent search is not limited to US patent documents but must include patent documents from other countries.

Problems with Classification Searches

The theory behind a classification search is based on the premise that examiners are receiving applications that are pertinent to their expertise based on classes and subclasses. Classifiers at the patent authorities are assigning codes to technology based on professional knowledge of technology or science. Initial classification is how patent applications are forwarded to the proper Art Units and thus to the patent examiners with the correct expertise. It would stand to reason, therefore, that classification systems are the perfect tool to search patent documents, applications and grants.

Unfortunately, this is not always the case for the patent researcher. Problems with the classification systems can be seen in the wide variances and interpretations of technology and science. There are four major classification systems: 1) United States Patent Classification (USPC); 2) Cooperative Patent Classification (CPC); 3) International Patent Classification (IPC); and the Japanese Patent Office’s F-Term and F-Index. These classification systems are either very broad or highly defined. The CPC and F-Term and F-Index are the most defined classification systems. The USPC is in the middle and will be defunct as of 2015. The IPC is very broad and updated every 5 years. The CPC is kept current in technological and scientific developments but classification of patent documents is not immediate, it may be a few months before a CPC code is assigned to the document. The USPC classification assignments are current at the time of publication and are retroactively updated. The downside to the USPC, besides its demise, is that updates to the USPC classes stopped in 2010. The researcher must be aware that using a classification system does come with its own set of problems.


Using keywords to begin a patent search can help familiarize a beginning inventor with patent documents and help identify useful patent classifications. There are limitations that the inventor needs to know about in both the keyword and classification searches. Keyword searching is an effective starting point as long as the inventor realizes it is just one part or rather one step in the patent document search strategy.

Quinn, Gene. “The Cost of Obtaining a Patent in the US.” IPWatchdog. (January 28, 2011), n.pag. Online: http://www.ipwatchdog.com/2011/01/28/the-cost-of-obtaining-patent/id=14668/ Accessed: March 4, 2014.
A searched performed on March 4, 2014, oref/”mad magazine”, in PatFT advanced search produced 11 patent grants that cite Mad Magazine in their reference documents (prior art).
Some of my favorite examples of problems with keyword searching: patent no. 7,683,276 uses the word “said” 278 times in 4 claims and the word “pivotal” is misspelled 3 times; and, in the original patent for Prozac®, patent no. 4,314,081, the chemical compound is misspelled in the title.
All searches were performed March 4, 2014.
An advanced search using – abst/electronic and abst/projectile and abst/impacts – in PatFT retrieves 4 patents. Patent no. 5,419,565 “Electrical device for detecting the location and speed or force of impact with a target” looks promising. This patent grant was classified in 473/455 ; 273/371; 273/374; 473/192; 473/462; 473/463. The other three retrieved patents were not relevant for this search.
Search query in PatFT: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=0&p=1&f=S&l=50&Query=abst%2Fdart+and+abst%2Felectronic+and+abst%2Fboard+&d=PTXT
An example I use in my workshops of this limitation is patent no. 7,003,941. The patent discloses a new propulsion system for satellites. In the “References Cited” patent no. 700,531 is cited as prior art. This patent is for a milk evaporator.