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Boolean operators are used as conjunctions to combine or exclude keywords in a search, resulting in more focused and productive results. Boolean operators save time and effort by eliminating search strings that are unrelated by greatly reducing and expanding the amount of records returned.. 

Examples of Boolean operators are: 

• AND
• OR
• NOT

AND

• Requires both terms to be in each item returned
• If one term is contained in the document and the other is not, the item is not included in the resulting list
• This narrows the search 
• Cats and dogs 
  • All items with 'cats' and 'dogs' in the document appear in search result

OR

• Either terms (or both) will be in the returned item
• This will broaden the search
• Cats OR Dogs
  • A search with 'cats' or 'dogs' will yield results the contain items focusing on each individual term
    • There will be documents focusing on cats but not dogs and documents focusing on dogs not cats
  • Documents with cats and dogs will be included in the search results in either order or number of uses

NOT

• The first term is searched and the second term is subtracted from the results
• If you need to search the not, that can be done by placing double quotes around it (<<>>)
• Be careful when using as your attempt to narrow the search may be too exclusive and eliminate good records
• Cats NOT Dogs 
  • Only retrieves items featuring 'cats' not 'dogs'

Using Parentheses

• Using the () to enclose search strategies will customize your results
• This will more accurately reflect your topic
• Search engines deal with search statements within the parentheses first, then apply any statements that are not enclosed
  • A search on (smoking or tobacco) and cancer returns articles containing: smoking and cancer; tobacco and cancer smoking; cancer, and tobacco; but does not return smoking or tobacco when cancer is not mentioned.