Boolean Searching
Boolean searching is based on a system of symbolic logic developed by George Boole, a 19th century English mathematician. Most computer databases and Internet search engines support Boolean searches. Boolean search techniques help reduce the number of irrelevant documents in the search results.
The power of Boolean searching is based on combinations of keywords with connecting terms called Boolean operators. The three basic operators are the terms AND, OR, and NOT. Many Internet search engines replace Boolean operators with symbols, for example + for AND, - for NOT.
The examples above illustrate general topics expressed with just two keywords. Actual search strings, which express complex topic ideas, may consist of several keywords and combinations of Boolean operators.
The thesis statement "Automobile air bags are not safe for children" might result in the search string:
automobiles AND air bags AND children AND safety
Most databases and major search engines support complex Boolean searches. If you have a complex search using more than one operator, you can nest your search terms, using parentheses. Search terms and operators included in parentheses will be searched first, then terms and operators outside the parentheses. A search for:
(ADD OR attention deficit disorder) AND college students
will search for documents containing either the acronym ADD or the words attention deficit disorder, then narrow the search results only to those documents that also contain the words college students.
These concepts are further illustrated in the Advanced Boolean Searching tutorial by Colorado State University Libraries.