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Database Searching: Refining Search Statements: Home

This guide provides information to assist our library users refine search statements for their academic research assignments.

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Refining search statements helps you find the most relevant results.  When results are relevant, they are on target or very close to the information being sought.  Complex search statements can be refined by adding words such as Boolean operators.

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Boolean Searching

  • Boolean searching is based on a system of symbolic logic developed by George Boole, a 19th century English mathematician.
  • Boolean search techniques help reduce the number of unrelated documents in the search results.
  • The three basic operators are the terms AND, OR, and NOT. 
  • Many internet search engines replace Boolean operators with symbols like + for AND, - for NOT.

•    And combines search terms so that each search result contains all of the terms.

For example, tires and brakes finds articles that contain both tires and brakes..

•    Or combines search terms so that each search result contains at least one of the terms.

For example, dentist or doctor finds results that contain either term or both terms.

•    Not excludes terms so that each search result does not contain any of the terms that follow it.

For example,city not town finds results that contain city but not town.

The following table illustrates the operation of Boolean terms:




Each result contains

Each result contains at

Results do not contain

all search terms.

least one search term.

the specified terms.

The search puppy and

The search puppy or kitten

The search puppy not

kitten finds items that

finds items that contain

kitten finds items that

contain both puppy

either puppy or items that

contain puppy but do not

and kitten.

contain kitten.

contain kitten.



 alt="Illustration of the Operation of  Boolean Terms"


Search Engine vs. Research Database

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Search engines conduct searches by using keywords.  Keywords are important words or phrases like nouns or noun phrases.  To choose your keywords leave out articles like a, an, or the, and prepositional or verb phrases like on, in or going to.

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