Troy University, TROY Global Campus Library Services

BOOLEAN OPERATORS

Named for George Boole, the proper use of of the everyday words and, or, and not, can make your searches more effective.

Most databases allow searches using the Boolean operators AND, OR, and NOT .

Use AND to limit search results, e.g., dog and cat.
Use OR to broaden a search, e.g., dog or cat or turtle
Use NOT to exclude results that include a particular term, e.g., (food additives) NOT pet. Use NOT with caution or you may exclude useful items.
Databases may also allow you to use other search operators such as NEAR or WITH. These terms are typically used to specify that a term appears "within X number of words" of another term. See the individual database for specific usage.

Most databases default the AND operator when you enter terms, e.g., if you enter the terms federal automotive laws the system will search on federal and automotive and laws; nevertheless, it is good practice for you to place the word "and" between terms—the reason for this is that the default may only search for your terms within a specified number words of each other, i.e., if they are within X words of each other. By you entering the word AND, you the database will search multiple places for your terms, e.g., the title, abstract, text. Use parenthesis to group your terms, e.g., (job or work or office) and stress.

The following Venn diagrams (named for John Venn), can help you to understand the use of Boolean.

RED = subject A, the concept teens. In an actual search, this concept might be represented by one or more search terms, e.g.,

youth
teen
teenager
adolescent

YELLOW = subject B, the concept of friends. In an actual search, this concept might be represented by one or more search terms, e.g.,

peer
friend

BLUE = subject C, the concept of recreation. In an actual search, this concept might be represented by one or more search terms, e.g.,

fun
activity
recreation
leisure

oror

andand

(and) not

and

(or) not

The important thing to remember when doing a search is to group, a.k.a. nest, your terms properly. REMEMBER: When you are interested in food for dogs or cats you need to search for (dog or cat) and food, not dog or cat and food.

(dog or cat) and food

This is the CORRECT search.

dog or cat and food

This is a "bad" search. If you don't tell the database how to search, it will usually perform the search by looking for "ands" first, then "ors"—or some other way that you did not intend. That is to say, it looks for cat and food, then it "ands" those results with dog. It is the equivalent of asking for: dog or (cat and food).

This page updated, spelling and links checked : Monday, December 10, 2007