LibGuides: Database Search Strategies: Boolean operators

What are Boolean operators?

Boolean operators form the basis of mathematical sets and database logic.

They tell the database how you want your keywords to be connected in the search.
You can use them to narrow or broaden your set of results.
Choose which to use based on what is logical to include or exclude for your specific need.

Why use Boolean operators?

To focus a search, particularly when your topic contains multiple search terms.
To connect various pieces of information to find exactly what you're looking for.

The three basic boolean operators are: AND, OR, and NOT. They must always be in ALL CAPS.

Boolean Operators Cheat Sheet

Using AND

Use AND in a search to:

narrow your results
tell the database that ALL search terms must be present in the resulting records

EXAMPLE:

The dark triangle in the middle of the Venn diagram below represents the result set for the search "cloning AND humans AND ethics"

Notes:

In many search engines the AND is implied.
All your search terms may be included in the results, but they may not be connected together the way you want.
The words may appear individually throughout the resulting records.

Using OR

Use OR in a search to:

combine related concepts or synonyms
broaden your results, telling the database that ANY of your search terms can be present in the resulting records

EXAMPLE:

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

Using NOT

Use NOT in a search to:

exclude words from your search
narrow your search, telling the database to ignore concepts that may be implied by your search terms
order does matter

EXAMPLE:

This search would exclude results that contain both peanut butter and jelly.

Caution: the NOT operator should be used sparingly and carefully as it may omit citations relevant to a search.

Search order

Be aware of the logical order in which words are connected when using Boolean operators:

Search terms combined with AND and OR can be entered in any order to retrieve the same results
The NOT operator excludes the search term directly after it
Databases usually recognize AND as the primary operator, and will connect concepts with AND together first.
When using the AND and OR operators in one search, enclose the OR terms in parentheses to force the computer to search for them first. Example: (symptoms OR treatments) AND diabetes