Boolean logic is used to construct search statements using logical connectors. This kind of searching allows you to relate multiple search terms together to more accurately express the concept you are seeking.
The three basic logical operators are
The NOT connector can be a very tricky connector to use effectively. It takes only one instance of a word to eliminate a document from your results set.
These three connectors are available in just about any electronic research tool. More sophisticated connectors are available on Lexis and Westlaw, and are also becoming more prevalent in Internet search engines as well. One limitation to the basic connectors is that they work on the entire document. If you want to find cases about attorneys committing malpractice, the search attorney AND malpractice is too broad. It will find cases that are about medical malpractice, but have the word "attorney" anywhere in the document - even if it is just a sentence saying "the plaintiff's attorney objected to the evidence."
Proximity connectors help with this difficulty. Common proximity operators are:
WITHIN - search terms must be within a specified number of words of each other. There is a great deal of variation among the search engines with this connector. Some search engines call it NEAR, some allow "w/n" where n is the number of words, some offer "w/s" for within the same sentence, and some offer "w/p" for within the same paragraph.
PRE - the first term must precede the second term. Some search engines call it BEFORE, and some allow specifying the maximum number of words in between the search terms, e.g. attorney pre/5 malpractice.
ADJ - adjacency or phrase searching requires the terms to appear directly adjacent to one another and in the specified order. Some search engines use quotation marks to indicate phrase searching.
Most search engines have some methods for dealing with word variations.
In all search engines, certain very common words such as on, under, with, will not be searched. Such words are called stop words, and each database has its own set of stop words. For example, the word "law" might be a useful term in a medical database, but it is so common that it might be a stop word in a legal database. For databases you use frequently, learn the stop words and avoid using those words in your searches.
Again, in all search engines, the order of connectors will dramatically affect your search results. A search in a job listing database for attorney AND (Chicago OR New York) is quite different than a search for (attorney AND Chicago) or New York.
The first search will retrieve job listings for attorneys in Chicago and for attorneys in New York. The second search will retrieve job listings for attorneys in Chicago, and all job listings in New York.
Every search engine, including those for Lexis and Westlaw, has its own "order of processing," the order in which it processes the connectors if you don't explicitly set the order. For the multitude of general search engines, the best strategy is to explicitly set the order of processing by using parentheses and to avoid combining too many different kinds of connectors.