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Starting your research

Boolean Operators

Boolean operators form the basis of mathematical sets and database logic.  They help determine HOW your terms are searched and connect your seach words together to either narrow or broaden your set of results.  While there are a number of boolean operators, the two most commonly used are: AND & OR.

The AND operator

Use AND in a search to:

  • narrow your results
  • tell the database that ALL search terms must be present in the resulting records
  • example: cloning AND humans AND ethics (the triangle in the middle of the Venn diagram below)

venn diagram

  • Be aware:  In many, but not all, databases, the AND is implied.
  • For example, Google automatically puts an AND in between your search terms.


The OR Operator

Use OR in a search to:

  • connect two or more similar concepts/synonyms
  • broaden your results, telling the database that ANY of your search terms can be present in the resulting records
  • contain your related terms in either a single search box or else by putting parentheses around them
  • example: (cloning OR genetics OR reproduction)

All three circles represent the result set for this search. It is a big set because any of those words are valid using the OR operator.

venn diagram


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