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Tarleton State University Libraries Unit 4
USING BOOLEAN OPERATORS
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image of venn diagram   Boolean Operators, which are also called connectors, are used in conjunction with search terms to broaden (expand) and narrow (restrict) searches to increase the number of relevant search results.

Since most searches involve more than one word, a means of combining terms, searching for synonyms, and eliminating terms is useful. Boolean operators allow these processes in online search tools such as library databases and Internet search engines. The three most commonly used boolean operators are explained below.


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HOW TO CREATE BOOLEAN SEARCHES
Explaining how to use boolean operators works best when using examples. Therefore, the following examples show how to use the boolean operators "and," "or," and "not." The examples incorporate search terms that might be used to locate information about how small groups make decisions. The purple-shaded areas indicate the amount of material that would be returned using each operator.

image of "and" search
   The boolean operator "and" is used to narrow (restrict) searches. Using this operator limits the search results to those containing all the search terms that have been connected with "and." In this example, only results containing the words "small group" and "decision-making" would be returned. Any number of terms can be combined using the operator "and."
     
image of "or" search   The boolean operator "or" is used to broaden searches to retrieve more results. Using this operator expands a search and returns records containing any of the terms or all the terms. In this example, some results would contain "small group," some would contain "decision-making," and some would contain both terms. This strategy is useful when using synonyms in searches.
     
image of "not" search
  
The boolean operator "not" is used to limit searches by eliminating terms from a search. Using this search restricts a search to increase precision. In this example, the results would contain the term "small group," but leave out results containing the term "decision-making," even if they appeared in the same record.

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Boolean operators can be combined in many ways and used separately or together. Often these combinations are more effective when also using a technique called "nesting," which is discussed on a separate page in this unit.

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Updated 7/2004