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Tips for Database Searching: Boolean Operators

Tips for conducting successful database searches.

Boolean Operators: What To Look For

Boolean operators form the basis of mathematical sets and database logic.

  • They connect your seach words together to either narrow or broaden your set of results.
  • The three basic boolean operators are: ANDOR, and NOT.

Why use Boolean operators?

  • To focus a search, particularly when your topic contains multiple search terms.
  • To connect various pieces of information to find exactly what you're looking for.
  • Example:
    second creation (title) AND wilmut and campbell (author) AND 2000 (year)

Boolean Operators: Using AND

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 below represents the result set for this search. It is a small set using AND, the combination of all three search words.

Be aware:  In many, but not all, databases, the AND is implied. 

  • For example, Google automatically puts an AND in between your search terms.
  • Though all your search terms are included in the results, they may not be connected together in the way you want.
  • For example, this search:  college students test anxiety  is translated to:  college AND students AND test AND anxiety. The words may appear individually throughout the resulting records.
  • You can search using phrases to make your results more specific.
  • For example:  "college students" AND "test anxiety". This way, the phrases show up in the results as you expect them to be.

Boolean Operators: Using OR

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.

Boolean Operators: Using NOT

Use NOT in a search to:

  • exclude words from your search
  • narrow your search, telling the database to ignore concepts that may be implied by your search terms
  • example:  cloning NOT sheep

Boolean Operators: 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)

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