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InfoSkills for Theology

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2.1. Boolean operators

What are Boolean operators?

Boolean operators allow you to combine search terms to create effective searches. They are named after George Boole, a 19th-century British mathematician who developed Boolean algebra – a system of logic fundamental to the way computers process information.

Boolean operators, or logical operators, are used to combine, include, or exclude search terms in a search statement. The three main operators are AND, OR, and NOT. Always capitalize them in database searches to ensure they are recognized correctly and not mistaken for regular words.

AND

Use AND in a search to:

  • Narrow your results
  • Instruct the database to return results that include every search term entered

EXAMPLE: cats AND dogs

The search returns a small result set, shown by the overlapping yellow area in the Venn diagram, which includes only results containing both cats and dogs.

Note In many – though not all – library databases, the Boolean operator AND is implied. This means that when you enter two or more words side by side, the database automatically treats them as if AND is placed between them. For example, human rights is interpreted as human AND rights.
OR

Use OR in a search to:

  • Broaden your results
  • Instruct the database to return results that contain at least one of the search terms 

EXAMPLE: cats OR dogs

The result set includes everything within both circles, creating a large set because any item containing at least one of the terms is retrieved.

NOT

Use NOT in a search to: 

  • Narrow your results
  • Instruct the database to leave out any results that include the term following the operator

EXAMPLE: cats NOT dogs

The result set includes everything in the first circle except the overlapping area, excluding any records that contain the terms in the second circle.

Boolean operators in action

Watch this 2:15-minute video to learn how Boolean operators can broaden and narrow database searches.

 Source: John M. Pfau Library

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