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Keyword vs. Subject Searching in Library Databases: Boolean Operators


AND retrieves records containing both terms,  as seen by the overlapping yellow areas below.  The yellow area represents records that contain the term both diet AND cancer.



OR retrieves records containing either one or both terms,  as seen by the entire yellow areas below.  The yellow area indicates records that contain one or both of the terms diet OR nutrition.



NOT excludes records containing the second term. Only the yellow area below would be included in search results.  This area indicates records that contain the word cancer, but NOT diet.

Boolean Connectors

Boolean connectors are all about sets. There are three little words that are used as Boolean connectors: AND, OR and NOT

Think of each keyword as having a set of results that are connected with it. These sets can be combined to produce a different set of results. You can also exclude certain sets from your results by using a Boolean connector.

The table below and the diagrams on the side explain how Boolean operators work.

Boolean Operator Examples

Boolean Operator




children and poverty

AND combines different terms when both must be present. Use AND to narrow a search.


children or youth

OR combines synonymous terms when at least one must be present. Use OR to broaden a search.


juvenile not crime

NOT eliminates irrelevant terms from a search. Use NOT when you want to exclude all records that contain a term.