Boolean, Truncation, and Wildcards
Boolean operators (or "connectors") allow a database search to be narrowed, broadened or made more precise. In Boolean searching, sets are created by inserting an operator between search terms. There are three Boolean operators: AND, OR, and NOT.
A short description of each operator is given below. In the diagrams below, the shaded areas represent those records which would be returned.
Note: The following search tools involve using various symbols. These symbols change depending on the database's vendor/interface you're dealing with, and the symbols may change over time within one of these vendors/interfaces. If you have any questions about what symbols are used in a database, check its "Help" section.
The AND operator is used for narrowing or focusing a search topic.
And specifies that both terms must be present on a record for it to be retrieved. Because of this, you will get fewer search results when using AND, but you will get more focused results.
Example: teenagers AND violence.
The operator OR is used for expanding or broadening a search topic.
By using the OR operator, the computer retrieves records that contain any of the connected terms.
OR is often used to include synonyms or related terms.
Example: teenagers OR juveniles.
By using NOT, the computer will retrieve records that contain the first term BUT NOT the second.
Example: teenagers not violence.
NOT is a bit more complicated and less-used than the first two connectors. Here's a detailed example of when to use NOT:
Suppose you are researching the ancient Sumerian city of Uruk. Since it's an uncommon name, you might just start your searching by doing this keyword search:
As soon as you get your results list back, you realize that something is wrong. Searching for Uruk by name gives you a ton of information on Lord of the Rings, because the "Uruk-Hai" is a type of evil creature in the classic fantasy trilogy. Your list is so full of Lord of the Rings information that you cannot even find one search result that has to do with Sumerian civilization. Therefore, you add a NOT term to your search:
Uruk NOT Tolkien
This added NOT term will get rid of anything that mentions J.R.R. Tolkien, the author of the Lord of the Rings, which will effectively remove all Lord of the Rings material and leave you with Sumerian information. You could instead search for Uruk AND Sumerian, but this would still give you Lord of the Rings results when it compares the story to ancient Sumerian writings, mythology, or languages, so the NOT term is more effective.
Be sure to use NOT sparingly and give careful thought to the term to be excluded. A poorly chosen NOT term will exclude good records! For example, doing the same search for Uruk NOT Rings would possibly remove Sumerian literature that involved ancient jewelry.
Multiple operators may be combined to create complex searches using nesting. Nesting involves enclosing search terms in parentheses to ensure operators are combined in the correct order. Always use the parentheses when mixing different operators!
Example: (teenagers or juveniles) and violence.
Truncation expands the search to locate all words beginning with the same root .
Example: teen* will return teen, teens, teenage, teenager, etc.)
A Wildcard is used in the middle of a word to match usually known variants of a term. A wildcard usually represents a single character,
Example: wom?n will return woman, women, and womyn.
Do you have any further questions about Boolean Connectors and other database tips and tricks? Chat with a Reference Librarian!