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College of Rehabilitation Sciences: Boolean Operators

Guide for OT, PT, RT, and MSc Rehab


  • Databases require mathematical rules in order to function
  • These mathematical functions are known as Boolean Operators
  • There are different operators, the most commonly used are AND, OR, NOT
  • Boolean operators allow for the combination of concepts in databases
    • AND focuses a search
    • OR expands a search
    • NOT removes from a search


  • OR is used to expand a concept
  • When searching you sometimes need to think of synonyms for a concept in order to capture all the information on that concept
  • For example, to capture all the information on heart attacks you would search heart attack [1] OR myocardial infarction [2] OR cardiac arrest [3]
  • The Venn diagram below illustrates how 3 sets of information, combined using OR, would give you the following sets of information: (1), (2), (3), (1,2), (1,3), (2,3), (1,2,3); all three sets of information would be in your results
  • What to watch for: do not overdo it when it comes to synonyms, only use the most logical; do not include broader concept terms, this will take away the focus of your search

venn diagram of OR operator


  • AND is used to focus a search
  • AND is used in searching when you want the results to contain all the concepts important to your research
  • For example, to capture information on the use of exercise by an elderly population as part of a fall prevention program you would search exercise AND elderly AND fall prevention
  • The Venn diagram below illustrates how 3 sets of information, combined using AND, would give you one set of information: (exercise [1], elderly [2] , fall prevention [3]); only the small centre set of information would be in your results, the one that contains all three elements
  • What to watch for: be careful of having too many concepts, if you AND too many ideas together you will end up with zero results



  • NOT excludes words from your search
  • NOT narrows your search, telling the database to ignore concepts that may be implied by your search terms
  • For example:  if you were searching for articles on nursing and education classes but you did not want articles on breast feeding would search: (nursing [1] AND "education classes [2]") NOT "breast feeding [3]" 
  • The Venn diagram below illustrates how you would use NOT to exclude information from a search, you would retrieve information that contains (nursing [1] and education classes [2]), the arrow head shaped set in the middle; the set (nursing [1], education classes [2], breast feeding [3]) would be excluded from the results
  • What to watch for: be careful using NOT as you may inadvertently exclude helpful articles from your search


  • Databases follow the commands you type in and return results based on those commands.
  • Databases follow a specific logical order when using Boolean operators: 
    • 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, you must enclose the words to be "ORed" together in parentheses so the database will combine those as a set before combining the AND concepts together.
  • Examples:
    • ethics AND (cloning OR reproductive techniques)
    • (ethics OR morals) AND (bioengineering OR cloning)
    • (nursing AND education classes) NOT (breast feeding)


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