Boolean Operators
 George Boole |
George Boole was an English mathematician who helped establish the modern field of mathematics called symbolic logic. Boolean logic uses words called operators. The three main operators are: AND, OR and NOT. Databases use Boolean logic to locate only those items that match your search. |
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The blue areas in the following diagrams represent the number of hits you would receive from doing a search using the Boolean operators AND or OR in the same database: using OR retrieves a large number of items:  using AND narrows the number of items returned:
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