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Database Search Tips: Connecting Words

a guide to ways to improve your searching in library databases

Boolean Operators

Boolean operators are words we use to connect search terms in database searches. They originated in a system of logic devised by mathematician George Boole (1815-1864). Boolean logic allows the user to combine words or phrases representing significant concepts in a keyword search of any online database. There are three primary Boolean operators:

AND - The AND operator narrows search results. Each time another concept is added using AND the search becomes more precise.

For Example: If we wanted articles which discuss dogs and cats, we might search our database by entering dogs and cats. The following venn diagram represents how our search is interpreted by the database.

Boolean operator for and image

NOTE: In many databases, AND is the implied operator. That is, many databases treat search terms input as dogs cats as dogs and cats.


OR - The OR operator expands the search by using related terms or synonyms. If your first search results in too few results, can you come up with terms to add in by using OR?

For example: if we wanted articles on dogs or cats, if we were researching housepets, we might enter search words dogs or cats. The following venn diagram is how the search would be interpreted.

Boolean operator OR image

NOT - The NOT operator is used to exlude unwanted records from our results.

For example, if you are researching information on dogs and you notice there are articles in your results which also discuss cats, you might edit your search to dogs not cats (that is, you want every article which discusses dogs, and everytime the same article discusses cats, you want to exclude it.) Here is how that search is interpreted.

Boolean operator NOT image


If you are searching several concepts and using Boolean operators you should group concepts together by using parentheses.

For example:

(dogs or canines) not (cats or felines)

(dogs or canines) and (stress or loneliness or anxiety)