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Discovering the "State of the Art": How To Conduct a Comprehensive Literature Search

How to conduct a comprehensive literature search for scientific or technical research

Subject / Keyword Searching

Subject or keyword searches are the most commonly used type of literature search. They are ideal for searching books, journal articles, and grey literature. Citation or reference tracking (see box at right) may also be employed and should generally be used for patent searching. In subject/keyword searching, try using different words and/or terms that define your problem until you locate at least one relevant document. See the General Search Tips tab for more info. Once you find a relevant document, you can find others like it by using the subject terms, descriptors, or keywords listed in the full record for the document. In some cases you will have to copy and paste the keywords into the search box, in others the keywords will be hot-linked.

Controlled indexing is a special feature of library databases. Web search engines like Google Scholar are machine indexed--indexing is done by a computer algorithm that basically counts the words in the document or web page. Library databases are indexed by subject specialists in the fields covered by the database. These specialists use a defined set of keywords or "controlled vocabulary" to describe what the document is about. Think of it as being similar to restaurant finders like GrubHub or Metromix where you can find restaurants serving Italian or Chinese cuisine regardless of whether the words "Chinese" or "Italian" appear anywhere in the name of the restaurant or their menu or website. Web search engines like Google would index them as "Italian" or Chinese" only if those words are used. With library databases, once you know the words or phases used by the indexers, you will be able to find all related documents.

Some examples of controlled indexing terms from different databases are shown below:

Treatment: Practical; Theoretical or Mathematical
Controlled Indexing: approximation theory; asynchronous machines; electromagnetic fields; equivalent circuits; finite element analysis; harmonic analysis; inductance; linear motors; magnetic circuits; stators
Uncontrolled Indexing: linear motor space harmonic analysis; lumped parameter; electromagnetic state; induction machine; higher space harmonic field component; electrodynamics state; linear machine; equivalent circuit parameter; polyharmonic machine model; space harmonic component; electromagnetic field distribution; finite element method; operational inductance; magnetic circuit saturation effect; phase current; machine field circuit model; frequency characteristics; stator spectral inductance
Classification Codes: B8330 Linear machines; B8310E Asynchronous machines; B0290T Finite element analysis; B0290F Interpolation and function approximation (numerical analysis); B2140 Inductors and transformers


Another important feature of library databases is the ability to combine searches to more easily create complex queries. This feature is usually found under "search history" or "search tools"--consult the help files for the database you're using for more details.

Citation Searching and Analysis using Web of Science

In addition to finding articles by topic or author, the Web of Science database allows researchers to explore scientific literature by citations and references. Web of Science allows you to follow references both backwards and forwards through time, so you can:

  • discover articles and papers citing a particular author or paper
  • determine the most influential articles and/or researchers in a particular topic by the number of times they've been cited
  • find related articles based on the number of shared references

The publisher of Web of Science provides a number of tutorials on how to use these features.

Citation / Reference Tracking

Citation or reference tracking is a very systematic approach and is ideal for patent searching. It also lends itself searching other types of literature.This is an iterative approach, using the references cited in one or more relevant documents to find other documents, then using the references cited in those documents to find more. After a few iterations, most of the documents found will duplicate what you already have. This approach works especially well with the Web of Science database and U.S. patent databases, which list other documents that cite the current document in addition to the references listed in the document. A typical method of reference tracking is:

  1. Using one of the databases, find a relevant document & note it in a spreadsheet
  2. Note all of the references in the spreadsheet. If you are using Web of Science or the U.S. Patent Office, also note all the documents that cite or reference your document. In Web of Science, click the "times cited" link for a list--in the USPTO database click the "referenced by" link.
  3. Repeat steps 1 & 2 for each document found in the references.
  4. Repeat steps 1 & 2 for all documents found in step 3. Additional iterations are usually not necessary.
  5. Review all discovered documents & discard those that are irrelevant.

Here's an example of a patent search for sunglasses combined with an mp3 player.

Pat Number Inventor Title References Cited References Cited
7219994 Jannard Eyeglass with MP3 player 1026272 May 1912 Leveque none none
Referenced By
none none
References Cited
1370806 March 1921 Gamer none none
Referenced By
5406340 Infant-to-toddler eye wear including head straps 04/11/95
6325507 Eyewear retention system extending across the top of a wearer's head 12/04/01
6966647 Telecommunications enabled eyeglass 11/22/05
7147324 Speaker mounts for eyeglass with MP3 player 12/12/06
7150526 Wireless interactive headset 12/19/06
7213917 Electronically enabled eyewear 05/08/07
7219994 Eyeglass with MP3 player 05/22/07
References Cited
D130310 November 1941 Monjar none none
Referenced By
D287021 Combined camera and eyeglasses 12/02/86
6325507 Eyewear retention system extending across the top of a wearer's head 12/04/01
6966647 Telecommunications enabled eyeglass 11/22/05
D523460 Headgear 06/20/06
7219994 Eyeglass with MP3 player 05/22/07
7264350 Multi-directional adjustment devices for speaker mounts for eyeglass with MP3 player 09/04/07
References Cited
2504524 April 1950 Hayward