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Boolean operators are a feature of many of the databases available from the Library and on the World Wide Web. Boolean Operators will help you make a better search by including more items that are relevant and fewer items that are irrelevant. The most commonly offered Boolean Operators are "OR", "AND" and "NOT".
In the examples below, the solid coloring in the venn diagrams represents the items that are retrieved.
The OR operator
The OR operator is similar to the union of sets. It is used to broaden a search or to complete a concept by including synonyms or variant terms for the same concept. In the example at right, set A, which is all items in the database that contain the word "apples" is put in an "or" relationship with set B, all items in the database which contain the word "Oranges".
The result is a set that includes all of the items in either A or B.
Examples using OR operators
Citrus OR Oranges OR Lemons OR Tangerines OR Grapefruit...
Ninja turtles OR Leonardo OR Michelangelo OR Donatello...
Ensure full retrieval for all the members of a class of items - be sure to include the name of the class of items (such as "citrus" or "ninja turtles").
HPLC OR high performance liquid chromatography
MRSA OR Methicillin-resistant Staphylococcus aureus
Search both the acronym or initialism and the name fully spelled out.
Search for English Language and foreign equivalents
dehydration OR hydration
fertility OR sterility
food security OR food insecurity
resistance OR susceptibility
burned OR unburned
You can sometimes use antonyms to fully express a concept
anthracnose ORApiognomonia OR Gnomonia
Use the name of the disease as well as the name(s) of the causal agent(s)
The more OR operators you use, the more material you will get. With some search engines, the OR operator is used by choosing "any of the words" or "with at least one of the words" when you search.
The AND Operator
The AND operator is similar to the intersection of sets. It is used to narrow a search or to make it more specific. In the example at right, set A, which is all items that contain the word "Apples" is put in an "and" relationship with set B, which is all items that contain the word "Oranges".
The result is a set that includes only those items that contain both the word apples AND the word oranges. Often in the sciences, the subject is of the pattern: The effect of A on B. This translates into the Boolean search A AND B.
altitude AND hypoxia
tannins AND beer
biodegredation AND beaches
rainfall AND deforestation AND Brazil
The more AND operators you use, the less material you will get. With some search engines, the AND operator is used by choosing "all of the words", "must contain", etc. when you search.
The NOT operator
The NOT operator is used to narrow a search but it is done by exclusion. In the example at right, set A, which is all items that contain the word "Apples" is put in an "not" relationship with set B, which is all items that contain the word "Oranges".
The result is a set that includes items with the word "Apples", but eliminates those which contain the word "Oranges". The NOT Operator should always be used with caution. The NOT operator is sometimes called "AND NOT".
heart disease NOT human
diabetes millitus NOT hyperglycemia
rheumatoid arthritis NOT juvenile
wound healing NOT plants
This bears repeating: use the NOT operator with caution. You risk eliminating relevant material that happens to incidentally mention the word you are "notting" out.
Boolean operators often can be used in combination. Examples:
(global positioning systems or gps) and automobiles
(laminitis or founder) and (equid or equids or equidae or horse or horses or mare or mares)
scientists and salaries not (education or academia or professors)
coastal sage scrub and (fire* OR postfire* OR burn* OR postburn* OR unburned OR pyrogenicity)
It is important to group the ORs with parenthesis when writing them out this way. Most of our databases support searching with boolean operators. The challenge here is to discover how each database website allows you to use them. Use their "help" pages to discover how to do it. Boolean searching is often available in an advanced search mode (called "power search", "guided search", "search plus" or something similar):
Note that in the above examples, you don't need the parenthesis since the search box structure takes care of that. Sometimes, you can just type in your boolean search (but be sure to use parenthesis):