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Database Search Tips: Boolean Operators

This guide provides general techniques and tips to help you search databases more effectively.

What are Boolean Operators and how can they help?

Boolean Operators are used to connect and define the relationship between your search terms. When searching electronic databases, you can use Boolean operators to either narrow or broaden your results list. The three Boolean operators are AND, OR, and NOT.

Why use Boolean operators?

  • To focus a search, particularly when your topic contains multiple search terms.
  • To use a single search for a topic or concept that may have multiple names.
  • To connect various pieces of information to find exactly what you're looking for.

In the examples below, AND, OR, and NOT are typed in capital letters.  This is to emphasize them in the examples.  When searching a database, you don't have to capitalize them. 

Using AND

Use AND to:

  • Narrow your search.
  • Tell the search engine that all results must contain all search terms.

  • Example search: cats AND dogs
  • The pink circle represents all articles containing the word cats; the blue circle represents all articles containing the word dogs.  The purple section in the center represents your search results: the articles that contain both terms.

Using OR

Use OR to:

  • Broaden your search. 
  • Tell the search engine that the results can include any or all of your search terms.

  • Example Search: cats OR dogs
  • The purple shape represents your results: all items that contain the word cats, all items that contain the word dogs, and all items that contain both terms.

You can also use OR to connect two or more similar concepts or search for something which has more than one name. 

  • For example: "online courses" OR "Web-based instruction" OR "distance education"

Using NOT

Use NOT to:

  • Narrow your search by excluding terms. 
  • Tell the search engine that results should include the first term but NOT the second. 

  • Example Search: cats NOT dogs
  • The purple shape represents the your results: the articles containing the word cats while excluding any article that also contains dogs.

Using NOT can help you further define the parameters of your search by excluding concepts that may often appear together but are not relevant to your research.

  • For example: cloning NOT sheep

Search Order

You can combine Boolean Operators to search for multiple things at the same time.  However, databases follow the commands as they're entered and return results based on those commands, so the order in which you type your search terms is somewhat important.

Databases usually recognize AND as the primary operator, and will connect concepts with AND together first.
If you use a combination of AND and OR operators in a search, enclose the words to be "ORed" together in parentheses.

Examples:

  • folk AND (music OR dance): Results will contain items with the terms folk music OR folk dance
  • ethics AND (cloning OR reproductive techniques)

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