Boolean Search Operators
The range of Boolean operators supported varies between search engines. Early search engines were entirely on Boolean logic, and although the use of Boolean is relatively rare today, most search engines continue to support it.
In more sophisticated search systems, user queries are sometime enhanced in an automated way to improve the quality of the query (which in turn improves the relevancy of results) by adding Boolean expressions.
Boolean logic defines conditions that are either met, or not met. If met, then the document will be contained in the results listing. Operators can be combined to create highly specific search clues.
COMMON BOOLEAN OPERATORS
Example: oak AND table AND chair
The document must contain all of these words.
Example: car OR automobile
The document qualifies if either (or both) of these words are present.
Example: golf NOT volkswagen
The word following the NOT operator must not be present in the document.
NEAR or NEAR/5
Example: symptom NEAR headache
NEAR is a specific form of AND which dictates that the specified terms must be within a certain number of words of each other. A NEAR operator will have a default number of words (typically 10) that defines the allowed separation, but this can be superceded by explicitly stating a number, for example NEAR/5.
NEXT or NEXT/5
Example: bill NEXT/3 clinton
NEXT is similar to NEAR, except that the words also have to occur in the stated order. So, the example above would match with Bill Clinton but not with Clinton, Bill
Example: (old OR elderly) AND (man OR gentleman)
As in mathematics, parentheses are used to dictate the order in which operators are resolved, the items inside the parentheses taking presidence.