Boolean operators (from XIXth century mathematician George Boole) are connectors used to create relationships between concepts. There are 3: and, or, not. Every online search tool (even Google) uses Boolean logic but not necessarily in the same way. Check the "Databases" and "Google" tabs above to find out more.
It's probably the most important search technique you can have in your toolkit!
This short tutorial from the University of Massachusetts in Boston is a good introduction to Boolean operators. Take 2 minutes to watch it then read the explanations below the video.
AND
AND links different concepts together.
The operator AND narrows your results, i.e., if you search for [cats and dogs] both terms must appear within the document or page.
Examples:
[olympics and fraud], [abortion and history and france], ["global migration" and "local economy"]
NOTE: All search engines use implicit AND which means that you don't have to write the word [and] in your search, they assume that's what you mean. E.g., [food health]
Most databases we subscribe to allow for full Boolean searches.
OR
OR links similar concepts together.
The operator OR will expand your results. If your query is [cats or dogs] that means that either one of the terms or both terms must be in the document or page.
Examples:
[fraud or corruption], [teenagers or adolescents], [house or habitat or home or accomodation]
NOTE: In Google you must capitalize OR or it will not be recognized as an operator. E.g., [teenagers OR adolescents]
Most databases we subscribe to allow for full Boolean searches.
NOT
The operator NOT excludes a word from the results. E.g., [vikings not football] will retrieve everything about the vikings (the big, tough guys) and not the football team.
Examples:
["government intervention" not europe], ["eating disorders" not anorexia]
NOTE: Google uses the minus sign [-] attached to the word or phrase to be excluded. E.g., [vikings -football].
Most databases we subscribe to allow for full Boolean searches.
Here are some examples on how you can use the Boolean operators in the same query.
Parenthesis can be used to separate search elements in a query. However, Google does not use parenthesis, you have to write the correct syntax using OR.
Note: Google does not use [and], it is implicit when you write words separated by a space. The space means [and]. Most databases followed Googe's example and also use the implicit [and]. We use it to demonstrate the type of operator needed.
SEARCHES USING DATABASES
"presidential elections" and 2016 and "united states"
"health benefits" and (veganism or vegetarianism) not flexitarianism
influence and violence and (tv or sports or media)
SAME SEARCHES USING GOOGLE
"presidential elections" 2016 "united states"
"health benefits" veganism OR vegetarianism -flexitarianism
influence violence tv OR sports OR media
There are several online tutorials on boolean logic. Here are a couple.
1. An animated tutorial from Colorado State University.
2. A flash tutorial about AND from the University of Illinois in Chicago.
http://www.newworldencyclopedia.org/entry/Image:Venn_diagram_cmyk.svg