Boolean Operators

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Boolean operators -- AND, OR and NOT -- are used to establish relationships between key words and keyword phrases. These operators can be used to expand or narrow a search and are often typed in ALL CAPS.  Some search engines presume AND occurs between words; some search engines understand + to mean AND; all search engines understand the word AND.

• The AND operator locates articles that contain all of the key words or phrases.
 
• Example: A query such as children AND computers returns articles that contain both key words.
• The OR operator locates articles that contain at least one of the key words or phrases.
 
• Example: A query such as hurricane OR tornado returns articles that contain one or both key words.
• The NOT operator eliminates articles that contain certain key words or phrases.
 
• Examples: A query such as basketball NOT college returns articles that contain the word basketball but not the word college.


California AND earthquake NOT "San Francisco" returns articles that contain the words California and earthquake but not the phrase San Francisco. This is an example of how to locate references to the various earthquakes in California, excluding those in San Francisco.

• Use AND and OR together to expand your search. AND has a higher precedence than OR, so you must enclose the OR words in parentheses.
 
• Example: health AND (kids OR children) will return articles that contain the words health and kids, or health and children.
• Use NOT and OR together to limit your search. NOT has a higher precedence than OR so a search using NOT and OR, produces results as described below.
 
• Example: (dog NOT cat) OR puppy will return articles that reference dog but don't contain cat, or contain puppy.

[adapted from SIRS http://ars.sirs.com]