Boolean searching is based on a system developed by George Boole, a 19th century mathematician. Most online databases and Internet search engines support Boolean searching. The power of Boolean searching is based on connecting keywords with Boolean operators. The three basic operators are AND, OR and NOT. This module goes over how they work.
ANDType AND between your keywords to narrow your search. The database or search engine will only retrieve those articles or web pages that contain both words. Using AND will decrease the number or hits or articles or web pages in your result list.
Example: school AND crime
Note: Some databases and search engines (such as Google and Craigslist) allow you to type a plus sign (+) in front of a keyword when doing a basic search. This works the same as AND.
ORType OR between your keywords to broaden your search. The database or search engine will retrieve those articles or web pages that contain at least one of these words. Using OR will increase the number of articles or web pages in your result list (especially if not used in combination with AND or NOT). Use OR between keywords that are synonyms or have similar meanings.
Example: baby OR infant
NOTType NOT before a keyword to exclude that keyword from your search. Using NOT will decrease the number of articles or web pages in your result list. The best use of NOT is when you are searching for a keyword that may have multiple meanings.
Example: Saturn NOT car
Combining Boolean OperatorsUse parentheses ( ) to keep combination searches in order. In the example below, the database or search engine will retrieve articles or web pages that must contain the word law and at least one of the words in parentheses.
This is also often referred to as "nesting." You can read more about nesting below.
Example: (ecstasy OR mdma) AND law
Nesting is a concept that works hand in hand with Boolean searching. If you have two subject terms that are similar in concecpt or share the same definition, you may want to nest them in parenthesis in order to group like terms.
In this example, the nested terms, ADD and ADHD, are both often used in the debate about the use of Ritalin in children. The database will first find everything about ADD or ADHD, then it will search for the other search terms within the entire body of literature on ADD and ADHD.
To look for an exact phrase, use quotation marks (" ") around the keywords.
Example:
Note: This works in most search engines as well. If you type an exact phrase without quotations when doing a basic search, most search engines will look for each word separately. In this example, quotation marks are not used, and the search results in every search term in green also being retrieved.
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The most common is asterisk (*) or less commonly, the question mark (?). If in doubt, check the "Help" screen for the truncation symbol.
In the examples that follow, the purple represents the original search, and the green represents possible results.
A good example of truncation:
Be careful NOT to end the stem or root of a word too early to retrieve too many results. A bad example of truncation:
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The Wildcard is usually an asterisk (*) or question mark (?).
When in doubt, check the Help File of the database or search engine.
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