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Norwalk Campus Library

Norwalk Mastering the Art of Library Research: Developing Essential Skills

Boolean Search

Keywords
 vs.
Subjects
  • natural language words describing your topic - good to start with
  
  • pre-defined "controlled vocabulary" words used to describe the content of each item (book, journal article) in a database
  • more flexible to search by - can combine together in many ways
  
  • less flexible to search by - need to know the exact controlled vocabulary term
  • database looks for keywords anywhere in the record - not necessarily connected together
  
  • database looks for subjects only in the subject heading or descriptor field, where the most relevant words appear
  • may yield too many or too few results
  
  • if too many results - also uses subheadings to focus on one aspect of the broader subject
  • may yield many irrelevant results
  
  • results usually very relevant to the topic

AND / OR

Use AND in a search to:

  • narrow your results
  • tell the database that ALL search terms must be present in the resulting records
  • example: cloning AND humans AND ethics

The purple triangle in the middle of the Venn diagram represents the result set for this search. It is a small set using AND--the combination of all three search words.

Use OR in a search to:

  • connect two or more similar concepts (synonyms)
  • broaden your results, telling the database that ANY of your search terms can be present in the resulting records
  • example: cloning OR genetics OR reproduction

All three circles represent the result set for this search. It is a big set because any of those words are valid using the OR operator.

Search Order

Databases follow commands you type in and return results based on those commands. Be aware of the logical order in which words are connected 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, enclose the words to be "ORed" together in parentheses.

Examples:

  • ethics AND (cloning OR reproductive techniques)
  • (ethic* OR moral*) AND (bioengineering OR cloning)