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Boolean searching is British mathematician George Boole's contribution to information retrieval. It has traditionally been used on databases, though it can also be used on many search engines. Boolean searching is a set of rules and operators that allow you to define exactly how you want your search done.
Boolean searching uses four logical operators:
Venn diagrams show the difference. The search will find results in the shaded area.
OR tells the search engine to look for either term in all the documents and pages it looks at. It is usually used with synonyms (e.g. women OR lady). The more words you include, the more results you will get. So,
will give you any documents or pages that have "women" or "pioneer" somewhere.
AND tells the search engine to look for any documents or pages that have both (or more) words. The more words you use, the fewer results you will get. So,
will only give you results that have both "women" and "pioneer" in them. Most search engines also support the use of the plus sign in place of AND:
NOT tells the search engine to look for any documents or pages containing the first term or terms, but not the term following the NOT operator. So,
tells the search engine that you want to find documents or pages that contain the word "women", but you don't want anything with the word "pioneer" in it. Most search engines also support the use of the minus sign in place of NOT:
NEAR tells the search engine that the words should be close to each other. Not all search engines support this operator. Those that do set the distance differently. See Search Engines for details. For example,
will make the search engine look for instances where "women" and "pioneer" are within ten words of each other.
There is a second version of Boolean searching supported by many search engines, sometimes called implied Boolean. Implied Boolean searching uses three logical operators:
Quotation marks (" ") put around the expression tells the search engine that you want to match the exact phrase. So,
tells the search engine to only look for instances where the words "women pioneers" are next to each other. Some search engines also use parentheses for this function:
Wild cards are one of the most powerful tools you can use in searching. They enable you to search for variations of a word. For example:
will give you any documents or pages that have "explor" as part of a word -- exploration, explore, exploring, explored, etc. Also,
will find both colour and color.
Wildcards vary from search engine to search engine, so read your search engine's "Help" or "Advanced" page. The asterisk (*) is the most common convention; % is also used.
Nesting, using parentheses, "forces" a search engine to do a search in a certain order. So,
will make the search engine sort through the results of "women OR lady OR female" first, then delete all the ones that have "pioneer."
The best way to use Boolean searching is to combine as many logical operators and keywords as possible to try to narrow the search. If this doesn't give enough results, then try reducing the number of keywords used in the search. By playing with the keywords you use, you can refine your searches to give the best results. For example:
If you do not use a Boolean operator, most search engines will assume that you meant to use "OR" or "AND" and give you results using one of those operators. Check the Help page of your search engine to find out which is used.
Different search engines work in different ways. Many have templates (forms) that help you with Boolean searching. Others use strict Boolean logic. Most, though, will use something in between.
Nearly all search engines support Boolean operators, with the notable exceptions of Google, LookSmart and Yahoo. For a detailed list of features supported by different search engines, visit Search Engine Watch's Search Features Charts: www.searchenginewatch.com/facts/article.php/2155981. For specific information on a particular search engine's features, look for information on that engine's "Help" or "Advanced" search pages.
To learn more about Boolean searching, visit the University of Albany Libraries' page Boolean Searching on the Internet: http://library.albany.edu/internet/boolean.html or Search Engine Watch's Web Searching Tips: http://searchenginewatch.com/facts.
Note: See also Search Help for tips on searching the Library and Archives Canada site.