Boolean Operators

Boolean operators are the logical operators of Boolean logic: AND, OR, and NOT. Boolean operators are often used as qualifiers in database searches.

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Hierarchy of Boolean Operators

A guide examining differences in the search procedures of different versions of WAIS offers an introduction to Boolean logic.

How to Search a WAIS Database

How to use Boolean operators in a search program.

Detail:

Boolean operators are used in Veronica and WAIS searches, and in a wide variety of Web search programs. In database situations, Boolean operators are also used in "if," "while," "do" and "for" statements.

Boolean operators look for comparisons or matching qualities. The three Boolean operators are:

• AND (logical conjunction), returns a match only if both terms appear
• OR (logical inclusion), returns a match if either term appears
• NOT (logical negation--equivalent to "and not"), returns a match if the first term matches and the second term does not.

The terms can be grouped within parentheses to form complex operators. A search with the complex operator pet .not.( cat .or. (dog .not. collie)) would find pets other than dogs and cats, but including collies.

Search terms that are separated by a space, with no operator present, may be handled either as though an OR or AND operator is present, depending on the particular search program. The order in which the expressions are implemented may vary from program to program, and some programs support Boolean operators but not parentheses.