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Boolean Operators - Overview
- 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
- OR expands a search
- AND focuses 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  OR myocardial infarction  OR cardiac arrest 
- The Venn diagram below illustrates how 3 sets of information, combined using OR, gives you all three sets of information 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.
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 , elderly  , fall prevention ); 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  AND "education classes ") NOT "breast feeding "
- The Venn diagram below illustrates how you would use NOT to exclude information from a search, you would retrieve information that contains (nursing  and education classes ), the arrow head shaped set in the middle; the set (nursing , education classes , breast feeding ) would be excluded from the results
What to watch for: be careful using NOT as you may inadvertently exclude helpful articles from your search
Rules for combining concepts using Boolean Operators
- 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.
- ethics AND (cloning OR reproductive techniques)
- (ethics OR morals) AND (bioengineering OR cloning)
- (nursing AND education classes) NOT (breast feeding)