Because of the creation of sets in online searching Boolean logic is deemed the best way to inc lude, exclude or combine these sets to retrieve the desired information. The English language is filled with ambiguities, shades of meaning and duplicative uses of words. Because of this we must try to narrow our search focus to be as accurate as possible in our retrieval. Another important thing to remember is that words sta nd for concepts that mean many different things to many different indexers. The development of a search strategy and the indexing of the system we are searching should match, but the match is rarely an exact or perfect one.
Boolean logic uses three basic 'operators' or limiters to manipulate sets.
OR is used to combine two or more terms that are synonymous, equivalent or variant terms. It is important in online searching to define the different terms used in a search, to be sure your retrieval is as complete as possible. AND is used to combine sets, the result is a set that contains only the items with both concepts. NOT is used to exclude a certain concept from a set. It is a very powerful tool and must be used with care.