A good online source can be found at: Boolean Logic. More resources are found in the Internet Literacy Links, or you can read on below.
A single word is all that is necessary to conduct an on-line search. Often,
however, that single word will return far too many files to efficiently review
and many will be of little value. To limit the number of files returned and to insure
that the files returned contain the information you want, you need to learn how
to use "Boolean operators".
Boolean operators are also called logical operators. They are used in database
searches as ways of qualifying search terms. The four most common Boolean operators
used in searches are AND (logical conjunction), OR (logical inclusion), XOR
(exclusive or), and NOT (logical negation).
The following variations of the logical operators AND and OR can be used:
Boolean operators are placed between words or sets of words. For example, submitting
the following terms will return all files refering to the Alaska pipeline:
|x AND y||x OR y|
|x And y||x Or y|
|x and y||x or y|
|x y ||(no equivalent)|
|x & y||x | y|
Alaska AND pipeline
If you used "OR" you would get all files with either the word Alsaka or the word
Some search enginges allow an astrix (*) to be used as a "wild card". That is, if you are not sure how
a name is spelled, or if the name is spelled in a variety of ways you might submit
something like the following search term used to return files containing information
about the anarchist, Mikhail Bakunin, whose name is spelled a variety of ways:
Naturally, you will get many useless hits, but you are sure to get files on Bakunin,
regardless of how his name is spelled.
"NOT" is used to restrict returns. To find records that do not contain a particular
word, place the word "not" before it. For example, "Mill not Stuart" would find all
the files on Mill that do not contain the word "Stuart."
You can also combine the "and," "or" and "not" commands. For example "John AND Mill AND NOT Stuart"
would find files on the famous father, not the famous son. Some search engines require
contiguous words to be joined by quotation marks, e.g. "John Mill", others join terms with
the underline character between the words, e.g., John_Mill. Still others require parentheses to join the terms,
e.g., (John Mill). Try them all and if none work, then that search engine doesn't support
The key to good returns on your search time is NARROW your search as
much as possible.