Boolean logic? what is it?
Answer
About Boolean Operators
Named after George Boole and his theory of symbolic logic, the tools known as Boolean Operators enable researchers to narrow or broaden their searching by connecting search terms in a specific way. The three most commonly used Boolean Operators are AND, OR, & NOT, and they are usually found in drop-down menus next to search boxes on the Advanced Search interfaces of online databases.
Use of the Boolean Operator AND between two or more search terms serves to narrow the list of results, because the search has been structured to retrieve materials that contain all of the terms provided. A search becomes more targeted with each term connected by the AND operator, which leads to a smaller number of items that fit the search criteria. For example, searching for apple AND banana will locate all materials that contain the words "apple" and "banana," and result in a list of materials that contain both words.
Meanwhile, searching for apple AND banana AND cherry will lead to an even smaller number of results because it will result in a list of materials that contain all three words.
Using the Boolean Operator "OR"
Use of the Boolean Operator OR between two or more search terms serves to broaden the list of results, because the search has been structured to retrieve materials that contain either of the terms provided. A search becomes less targeted with each term connected by the OR operator, which leads to a larger number of items that fit the search criteria. The OR operator is especially useful when employing search terms that are synonymous with each other.
For example, searching for dog OR canine will locate all materials that contain the words “dog” or “canine” and result in a list of materials that contain either word.
Use of the Boolean Operator NOT between two or more search terms serves to narrow the list of results, because the search has been structured to disregard materials that contain one or more of the terms provided. A search becomes more targeted with each term connected by the NOT operator, which leads to a smaller number of items that fit the search criteria.
For example, searching for twins NOT baseball will locate materials that contain the word “twins” but do not contain the word “baseball.”
Use of the NOT operator can sometimes lead to the exclusion of materials that may actually be relevant to the researcher’s needs. For instance, someone who is looking for information about identical twins and searches for twins NOT baseball in order to exclude articles about the Minnesota sports team will also exclude articles about twins who play baseball. It is important to consider what effect the use of the NOT operator will have on a search before employing this particular tool.
Some researchers elect to use more than one Boolean Operator at a time for a more targeted search. In these cases, using parentheses to cluster terms in one search box will indicate which grouping should be applied to the search first.
For example, searching for sales AND (car OR automobile) will locate materials that contain the word “sales” and either “car” or “automobile."
Searching for student AND (graduate NOT undergraduate) will locate materials that contain the words “student” and “graduate” but will exclude materials that contain the word “undergraduate.”
Searching for (college OR university) NOT junior will locate materials that contain either the word “college” or the word “university” but exclude any materials that contain the word “junior.”