A system of logic developed by the English mathematician George Boole (1815-64) that allows the user to combine words or phrases representing significant concepts when searching an online catalog or bibliographic database by keywords. Three logical commands (sometimes called "operators") are available in most search software:

The OR command is used to expand retrieval by including synonyms and related terms in the query. See also: logical sum. Search statement: violence or conflict or aggression

The AND command is used to narrow search results. Each time another concept is added using "and," the search becomes more specific. In some online catalogs and databases, the "and" command is implicit (no need to type it between terms). In other interfaces, keywords will be searched as a phrase if not separated by "and." See also: logical product. Search statement: violence and television and children

The NOT command is used to exclude unwanted records from search results. See also: logical difference. Search statement: television not news

When two different Boolean commands are used in the same search statement, parentheses must be included to indicate the sequence in which they are to be executed (syntax). This technique is called nesting. Search statement: television and (violence or aggression) and children

For a detailed discussion of Boolean logic, please see the entry by Gwyneth Tseng in the International Encyclopedia of Information and Library Science (Routledge, 2003). Click here to see Boolean logic illustrated with Venn diagrams, and here to learn how it works in computer searching, courtesy of HowStuffWorks.

See also: proximity and truncation.


From ODLIS, Online Dictionary of Library and Information Science by Joan M. Reitz
http://lu.com/odlis/odlis_c.cfm