How to conduct a Patent Search?

What are different strategies for patent search?

Various strategies of the patent search include:-

Keyword-based search

Most of the inventors begin their search by using a few keywords from their invention. The searcher goes to any of the free patent databases and types the keywords from the invention. So, the searcher may not go through the entire list of the patents, but only a list of patents related to his area of interest. The keywords should be such that it describes:

  •  Purpose of the invention
  •  The proximate or essential function of the invention
  •  Composition
  •  End result

One issue with the keyword-based searches is that the inventor’s semantics may not match with the semantics or terminologies of the others. The patent drafter is allowed to create his own terminology to describe his invention. For example, a mouse trap can also be used as a ‘rodent extermination device’ by some drafters. Another issue is that some of the US applications are from other nations. The foreign entity applications may contain misspelled words e.g. colour in place of color. This is the yet another issue with the keyword-based searches as the search results are limited to the terminologies used by the searchers and exclude the misspelled words.

Class-based search

In general, each patent application document is arranged by the examiners of patent offices or other people based on the technical features of the inventions. They arrange documents using a patent classification to classify the content of patents in a uniform manner. The classification of the patent in a uniform manner helps to quickly find a document disclosing the invention identical or similar to the invention for which a patent is claimed. The same document may be classified into several classes.

A patent classification is fixed under an agreement among people, otherwise it is useless.

There are various agencies which classify the patent application. Some of these classifications are as follows

  • The International Patent Classification (IPC) which is agreed internationally.
  • The United States Patent Classification (USPC) which is fixed by the United States Patent and Trademark Office         (USPTO).
  • The European Classification (ECLA) which is based on the IPC but adapted by the European Patent Office (EPO)       to its own requirements.
  • The Derwent classification system which is fixed by an enterprise.

Most of these classification agencies organize the patent documents and some technical and non-technical documents based on common subject matter. Each subject matter division includes a major component called as a class and a minor component called a subclass. Every class has a unique alphanumeric identifier, as do most subclasses. The unique identifier is referred to as a classification symbol. A classification assigned to a document associates the document to the class and subclass identified by the classification.

Every class shares some similar properties. The properties are:

  • Every class has a title that describes the subject matter found in the documents.
  • Every class has an identifier that uniquely defines a class.
  • Every class has a definition that describes the details of the subject matter.

Classes are mutually exclusive i.e. the subject matter provided by one class does not overlap with the subject matter provided by another class. So, class-based searches are the searches based on the class of the patent.

IPC based Search

The International Patent Classification (IPC) is a hierarchical collection of alphanumeric symbols for the classification of patents representing 70,000 subdivisions of groups. The World Intellectual Property Organization (WIPO) maintains the IPC. The IPC’s are basically a comprehensive subject classification system applied to all patents by the patent issuing authorities.

IPCs can be used to enhance the patent search. It is helpful in retrieving the records in a case when the invention is described in the ways that one might not have thought and included in a word search. The IPC based search maximizes the effectiveness of searching.

Here is an example of the hierarchy of IPC codes taken from the WIPO website.

H 04 B 7/00 Radio transmission systems, i.e. using radiation field
H 04 B 7/208 Frequency-division multiple access


If one is looking specifically for records relating to Electric transmission systems for frequency-division multiple access, he should search the complete IPC Code: H04B7/208.

If one is looking for records relating to Electric radio transmission systems, he should search the IPC Code: H04B7/00.

If one is searching for records relating to any type of electric communication technique transmission, he/she should search the ‘subclass’ level of the IPC Code: H04B.

If one requires a general search to identify all records relating to Electric Communication Technique, he/she can search the class level of the IPC code: H04.

US Class-Based Search

U.S. Patent Classification System has over 400 classes, each having a title descriptive of its subject matter and each being identified by a class number. In general, each of the class is subdivided into a number of subclasses and each subclass has a descriptive title and a subclass number. The subclass number may have alpha characters and may also contain an integral number or a decimal portion. For example, 418/61.1 identifies Class 418 and Subclass 61.1.

All of the class and subclass titles are present and elaborated in the Manual of Classification. The manual of Classification has different parts which are as:

  • Overview of the classification system, a hierarchical arrangement of class titles organized into four main groups by related subject matter,
  • A list, in numerical order, by art unit indicating the classification(s) assigned to each,
  • A list of classifications in numerical order by class number giving the class title, the art unit to which the art is assigned, and the examiner search room in which the art can be found,
  • A list of classes in alphabetical order by class title with associated class numbers, a class schedule for plants, a class schedules for utility patent classes arranged in numerical sequence by class number and a class schedules for the Design classes.

ECLA Sub-Divisions

ECLA i.e. European Classification is an enhancement to the IPC. It is homogeneous and systematic. The IPC has 67,000 sub-divisions; the ECLA classification has around 134,000. Moreover, ECLA is revised continuously and the corresponding document is re-classified.

Its major features include:-

Highly skilled personnel

ECLA classes are only assigned by the European Patent Organization (EPO) examining corps. It means that the relevance of the system and the accuracy of its use is maintained and ensured by a small body of highly trained individuals.

In contrast, IPC classes are applied by examiners all over the world, many of whom have insufficient training. Also, the IPC class searching can result in poor search quality due to inconsistent indexing efforts. So, searchers can feel more confident when searching with ECLA classes.

Narrow class definitions

ECLA classes are defined to split the large IPC sub-groups into even smaller divisions. The IPC has 67,000 subdivisions as of 2005; the ECLA classification had around 129,000.

Accelerated revision schedules

ECLA is a flexible classification system that changes and grows with fast-moving technologies in contrast to the inflexible 5-year revision schedule of the IPC; however, since the institution of IPC reform in January 2006, advanced IPC codes now offer the same advantage as ECLA.

Back-file updates

EPO examiners re-index their back-file of documents for major patenting authorities to keep ECLA searching current and accurate. Originally, this feature was in contrast to IPC revisions. However, since IPC reforms were enacted in January 2006, electronic records for already-published documents will be continually updated as IPC class definitions change.

Non-Patent literature indexing

EPO examiners use ECLA codes to classify non-patent literature documents they come across during examination. These documents are part of the EPO’s searchable files, and are currently loaded into some free (esp@cenet) and commercial (Questel-Orbit) search providers as well.

Disadvantage or other considerations to account for when searching using ECLA include:

ECLA classes are not published in the document when it is issued; they are assigned as in-computer codes by European patent examiners. Moreover, they usually become available several months after publication. So, the ECLA classes cannot be used to retrieve very recently issued documents.

CPC Classification

The European Classification (ECLA) System was replaced by Cooperative Patent Classification (CPC) on January 01, 2013. The CPC has a hierarchical structure and is based on the International Patent Classification (IPC). It is a patent classification system jointly developed by the European Patent Office (EPO) and the United States Patent and Trademark Office (USPTO).

Being a bilateral system, the CPC combines the classification practices of the two offices, thereby allowing the searchers to retrieve the relevant prior art efficiently. Initially, the CPC system was based on the former European Classification system (ECLA) which was an extension of the International Patent Classification (IPC) and kept all the properties of the IPC. The IPC has 70,000 entries, the ECLA has 160,000, and however, the hierarchical structure of the CPC contains approximately 250,000 groups. The CPC has a huge collection of indexing codes in the 2000 series.

Each classification term consists of a symbol such as “A01B33/00”. The first letter is the “section symbol” consisting of a letter. For example, the letter “A” represents “Human Necessities”, the letter “H” represents “Electricity”, the letter “Y” represents emerging cross-sectional technologies etc. This is followed by a two digit number to give a “class symbol”. For example, “A01” represents “Agriculture; forestry; animal husbandry; trapping; fishing”. The final letter makes up the “subclass”. For example, “A01B” represents “soil working in agriculture or forestry, parts, details, or accessories of agricultural machines or implements’. The subclass is then followed by a 1 to 3 digit “group” number, an oblique stroke and a number of at least two digits representing a “main group” (“00”) or “subgroup”.

If one is familiar with a particular CPC symbol or have found one on some documents after a quick search based on keywords, he can check its description by entering it in the search field and clicking on Search.

One can also search for the CPC symbols by starting with a simple query in the search field, followed by a click on Search. One can even restart a search with specific symbols.

Inventor based search

Patent searching is done using the inventor’s name. The inventor based search is useful where the searcher knows that a particular inventor has filed a lot of patent application in a particular sub-domain. The searcher may like to extract all the patent application filed by that inventor in that sub-domain. Most of the databases give the option to search for the patents by inventor’s name using any combination of name, city, state or country and a range of dates. For example, if the searcher wants to search by the inventor’s name using the USPTO, then enter the inventor’s name in any of the following formats:





The City of the Inventor at the time of publication should be mentioned. The US state of residence of the inventor at the time of publication should be written. However, if the inventor resides outside US, there is no state field. The country of residence of the inventor at the time of publication should be mentioned. However, if the inventor resides in the US, there is no country field.

Assignee based search

Another way to search the patent is through its assignee name. The assignee can be an individual or a group of individuals to whom the patent to be searched has been issued. In case, when the assignee is not an individual, then the patent is assigned to either a group of individuals or to the company/firm. For example, a patent for application software built and managed by Microsoft Corporation may be assigned to the Microsoft Corporation instead of an individual.

One can search the patent using the assignee based search by using any combination of the name of the assignee, the name of the firm, and state or country in which the assignee resides.

Concept-based search

Yet another way to search for a patent application is by using a concept-based search. A concept based search is the search that uses relationship and structure between different elements and method steps to find relevant prior art. This is the searching of the patent documents having the same or related concepts as the interested patent (patent for which the prior arts are searched). Also, the searching involves finding the prior arts based on the same technology timeline and concept.

For example, if an inventor has an idea of optimizing the battery in electronic devices using a combined battery-ultra-capacitor energy storage system, then he/she should look for the prior arts based on or related to the combined battery-ultra-capacitor energy storage system.

Jurisdiction based search

Patent Searching is also done using jurisdiction based search. The Jurisdiction based search involves searching according to the laws and policies pertaining to different countries. Each country formulates different rules for patent documentation and searching and hence patent searching is done accordingly. The jurisdiction-based search establishes whether or not, one can legally commercialize the product and target a specific market.

Citation-based search

Another way to search the patent is by using a citation-based search. Citations are documents that are linked together and one document mentions another as having related content. The citations are listed in the patent document.

The citation of one or more patents by a patent is useful because of two reasons.

The cited patents are the patents the applicant disclosed it as prior art known to him or these can be the patents that are found by the examiner during the search. So, if the inventor is aware of prior arts, then during filing of his application, he is required to disclose these known patents in his patent application.

The second scenario is that the inventor had no knowledge of the earlier patents, but the examiner found it as relevant art during the search.

There are two types of citations. When two documents are linked together in a way that both can be alternatively referred to as citations, and then the terms used to clarify the relationship are a backward citation and forward citation. The backward citation is the document that was published earlier and which appears on the newer document’s front page. The newer document is referred to as forwarding citation or citing the document.

Citation-based searching is an excellent way to discover other patents which are closely related to the main patent document. Another benefit of a citation search is that it can expose new relevant documents that are not found during the keyword-based search or any other searching techniques.

For example, if an inventor has decided to draft his invention regarding a method and system for battery optimization in electronic devices, and if he is aware of the prior arts regarding battery optimization of any device, then he should mention the list of all the citations (prior arts) during filing of his application. If the inventor does not disclose the citations or discloses a few related patents, then the examiner may disclose some related patents during the search conducted by him.

Date based search

In order to search for a patent application, the searcher can perform a date-based search. In general, the important dates associated with a patent application include a priority date, a filing date, a publication date and an issue date. The filing date is the date on which the patent application is filed by the inventor to get the patent granted. The patent applications are published 18 months after the earliest priority date of the application. Prior to publication, the patent application remains purely confidential to the patent office. But after the publication, depending upon local rules, certain parts of the patent application may remain confidential, but it is common for all communications between an applicant and the patent office to be publicly available. Therefore, the publication of the patent application marks the date at which the patent application is publicly available and forms the prior art for other patent applications worldwide.

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