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Finding Articles & Using Databases: Boolean Searching

Using Boolean Operators - Advanced Search Techniques

Using the concept of Venn Diagrams, here is a visual of how these operators behave:

AND operator 2 keywords

  • Your returns here may be high, but it’s always easier to limit results than it is to expand them.
  • By starting with a large result, additional keywords can be added to help hone in on the topic.
  • A phrase search could have also been conducted: "military aviation".

AND operator 3 keywords

  • Now it becomes clearer that the topic is safety in military aviation. Any articles returned that have all three keywords present are likely to be highly relevant.
  • These results can be filtered further by telling the database (via the dropdowns offered in most catalogs and databases) that you only want to see results where these three words are in the subject or the abstract.
  • This stairstep approach almost guarantees highly relevant results without excluding something that might be important to your topic.

OR Operator

  • Aircraft and airplane could likely be interchangeable, so using the OR operator asks the database to return any results that have either the word aircraft or airplane in the article.
  • As these are broad terms, the results will be substantial, but you can always pare down from there using the AND strategy.

NOT operator

  • Let’s say you only wanted to study commercial aviation, but the top results contained information on military operations, NASA or the US Air Force. While you could use the word commercial as an additional keyword (using AND), you can also drop all the results relative to the military by using the NOT operator.


Named for English mathematician George Boole (1815 - 1864), Boolean operators are used to connect and define the relationship between the words in your search. The three operators most commonly used in Library databases are:

AND All terms listed must be contained in the citation; abstract; or in the case of a full-text database, the article. LIMITS RESULTS nursing AND vaccine will find results that have both words present.
OR Just one of the listed terms will need to be present in the citation, abstract or article. EXPANDS RESULTS dog OR canine keywords in your result set will have either the word dog or the word canine.
NOT The word following the NOT will be excluded. LIMITS RESULTS bee NOT spelling will find results on the insects but not the competitions.


Keep in mind the operators AND / OR are completely opposite to how we use them in everyday language:

    • AND normally suggests more (e.g. I can have cake AND ice cream). But in databases, AND is a limiter because this instructs the database to return only articles that contain BOTH words.

  • OR in every day language means choosing one option over another (e.g. I can register as a democrat or a republican). The use of OR can greatly expand results because the database will return articles that contain ANY of the keywords.

Also, there are symbols and punctuation that help further refine results:

  • Putting keywords in quotes will tell the database to search for a phrase, this means the words will either be next to each other or within close proximity.
    • Example: "marketing ethics" will look for these words in this order. If the quotes were not there, the database would treat these words as an AND, and look for articles that contain both of the words marketing and ethics anywhere in the article.
    • For this reason, phrase searching is a great way to NARROW results if you are searching for a concept.
  • Putting an asterisk (*) behind the root of the word will return all versions of that word.
    • Example: global* will return results that contain the words: global, globally, globalization, globalize etc.
    • For this reason, the use of the * (also known as truncation or proximity operator) is a great way to EXPAND results.

These operators work in many commercial search engines, websites and databases.

  • You usually have to enter the operators in CAPS for them to be recognized
  • Sometimes, databases and search engines (e.g. Google) have created a form for you to search using Boolean operators without having to type them in. This can usually be found in the Advanced Search page of the website.
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