Tuesday, April 12, 2005

ANDs and ORs and NOTs, oh my!

Boolean Operators and Venn Diagrams

Many bibliographic databases use Boolean operators as the building blocks for the construction of search strategies, from the simplest to the most complex. Boolean operators should bring back memories of your high school algebra days where together with Venn diagrams, the world of the algebraic equation was illuminated.

AND, OR, and NOT are the Boolean operators we’re concerned with and I’m going to use a Venn diagram to illustrate what is meant.

Boolean operators are used to combine sets. In our case, the sets are made up of search terms. Using Boolean operators, we can construct complex equations.

My Venn diagram shows all the possible relationships for two sets – Set 1 and Set 2:

A – the records found exclusively in Set 1
B – the records found exclusively in Set 2
C – the records found in both Set 1 and Set 2
D – the records not found in either set

As a searcher, you can use these operators to indicate how you want the sets of subject terms you’ve created to be combined.

AND retrieves records containing all the terms
OR retrieves records containing one or more of the terms
NOT retrieves records containing one term but not the other


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