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  ORmyocardial infarction  OR cardiac arrest 
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
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 exerciseANDelderlyAND 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)