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Using the Search Operators AND, OR, and NOT
How to Write Boolean Expressions
The operators listed on these pages are described as they are used in EBSCOhost and Gale databases. Some other databases may use symbols rather than words, e.g., "&" instead of "AND," or they may call the operators by different names, although the function is the same. Check the help for a database to find more particulars. Our library has a short video that shows you how to do Boolean searches in a database. Check it out!
Boolean searching is a technique of searching by linking concepts together with commands known as Boolean operators. Examples of Boolean operators are "AND" and "OR." Boolean searching is a powerful tool for refining a search to produce a highly focused result.
Let's say, for example, that we want information about sports-related injuries. We could search for the phrase, "sports-related injuries," but that would leave out documents that say "injuries due to sports." Instead, we may use the Boolean operator "AND" to link together the concepts "sports" and "injuries." This could be expressed in a diagram:
In the illustration, the left circle represents all the documents which contain the word "sports," and the right circle represents all the documents which contain the word "injuries." Documents which contain both words are represented by the area of overlap where the two circles intersect. The search "sports AND injuries" would retrieve documents which contain both words.
Note: Some databases automatically combine search terms with AND.
The "AND" operator is the most commonly used one, because it makes the resulting set smaller and more focused. Another operator which makes the resulting set smaller is "NOT." "NOT" excludes a term from the resulting list. "Sports NOT golf," for example, subtracts all "sports" documents that include the word "golf." We might retrieve documents about the Olympics, football, tennis, or curling, but none of the documents in the resulting set would contain the word, "golf."
An operator which makes the resulting set larger is "OR." When we searched for the word "injuries," we might have missed documents which described "wounds" or "trauma" without using the word "injuries." To find all of these we might search for "injury OR trauma OR wounds." "OR" broadens the resulting set to include documents which contain at least one of these words. In the diagram below, all of the sets represented by circles would be part of the result set.
Note: Some databases automatically combine search terms with OR.
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Last Updated: Feb 7, 2018 12:01 PM
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