A Primer in Boolean Logic
The Internet is a vast computer database. As such, its contents must be searched according to the rules of computer database searching. Much database searching is based on the principles of Boolean logic. Boolean logic refers to the logical relationship among search terms, and is named for the British-born Irish mathematician George Boole. On Internet search engines, the options for constructing logical relationships among search terms often modify the traditional practice of Boolean searching. This will be covered in the section below, Boolean Searching on the Internet. Boolean logic consists of three logical operators:
Each operator can be visually described by using Venn diagrams, as shown below.
college OR university
Question: I would like information about college.
• In this search, we will retrieve records in which AT LEAST ONE of the search terms is present. We are searching on the terms college and also university since documents containing either of these words might be relevant. • This is illustrated by:
• the shaded circle with the word college representing all the records that contain the word "college" • the shaded circle with the word university representing all the records that contain the word "university" • the shaded overlap area representing all the records that contain both "college" and "university" OR logic is most commonly used to search for synonymous terms or concepts. Here is an example of how OR logic works:
|Search terms |Results |
|college |396,482 |
|university |590,791 |
|college OR university |819,214 |
OR logic collates the results to retrieve all the unique records containing one term, the other term, or both of them. The more terms or concepts we combine in a search with OR logic, the more results we will retrieve. [pic]
college OR university OR campus
|Search terms |Results | |college |396,482 | |university |590,791 | |college OR university |819,214 | |college OR university OR campus |929,677 |
poverty AND crime
Question: I'm interested in the relationship between poverty and crime. • In this search, we retrieve records in which BOTH of the search terms are present • This is illustrated by the shaded area overlapping the two circles representing all the records that contain both the word "poverty" and the word "crime" • Notice how we do not retrieve any records with only "poverty" or only "crime" Here is an example of how AND logic works:
|Search terms |Results |
|poverty |76,342 |
|crime |348,252 |
|poverty AND crime |12,998 |
The more terms or concepts we combine in a search with AND logic, the fewer results we will retrieve. [pic]
poverty AND crime AND gender
|Search terms |Results | |poverty |76,342 | |crime |348,252 | |poverty AND crime |12,998 | |poverty AND crime AND gender |1,220 |
In addition: a very few search engines make use of the proximity operator NEAR. A proximity operator determines the closeness of terms within the text of a source document. NEAR is a restrictive AND. The closeness of the search terms is determined by the particular search engine. Most search engines default to proximity searching by default.
cats NOT dogs
Question: I want information about cats, but I don't...