Boolean Operators
Boolean operators are the words "AND", "OR" and "NOT". When used in library databases (typed between your keywords) they can make your search more precise.
AND narrows a search by telling the database that ALL terms used must be found in order for it to appear in your results list. Search for two or more concepts by combining them with AND.
For instance, if you want to search by cats and dogs, you will only get results where those are both present.
Cats AND dogs
OR will expand your search results so all results must contain at least one, if not more, of your defined terms.
For instance, if you want to search by cats or dogs, you will get results with either or both are present.
Cats OR Dogs
NOT excludes terms so that your search results do not contain any of the terms that follow it. This can be useful when:
- you are interested in a very specific aspect of a topic (letting you weed out the issues that you're not planning on addressing)
- when you want to exclude a certain type of material (e.g., a conference paper, book review, etc.)
Use NOT with caution as good items can be eliminated from your results.
For instance, searching for cats not dogs will return results on cats, but not those dealing with dogs.
cats NOT dogs
Parentheses are used to communicate to the database the order in which it should resolve the AND, OR, & NOT statements by nesting query terms.
You can enclose search terms and their operators in parentheses to specify the order in which they are interpreted. Information within parentheses is read first, then information outside parentheses is read next.
For example, when you enter...
(carpenter bee OR honey bee) AND pollination
... the search engine retrieves results containing the word carpenter bee or the word honey bee together with the word pollination.
If there are nested parentheses, the search engine processes the innermost parenthetical expression first, then the next, and so on until the entire query has been interpreted.
Quotation marks are used around a phrase that needs to be returned in that exact order.
For instance, “carpenter bee” will only return results that contain the exact phrase ‘carpenter bee.’ If you do not use quotation marks around phrases, each word in the phrase will be treated separately as if you used AND between each word. For example: a search on carpenter bee may display results that contain the words ‘carpenter’ and ‘bee’ but not necessarily in that order. These are not needed in all cases since a lot of times databases recognize 'carpenter bee' and other common terms and will search them together without the need or quotation marks.
Boolean Operators Video