Boolean Searching on the Internet

[A Primer in Boolean Logic] [Boolean Searching on the Internet]

[Quick Comparison Chart] [Where to Search]
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 mathematician George Boole.
On Internet search engines, the options to construct logical relationships among search terms extend beyond 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:
OR
AND
NOT
Each operator can be visually described by using Venn diagrams, as shown below.

or

college OR university

and

college AND university

not

college NOT university
Query:    I would like information about college.
I would enter the search string - information and (college or university)

Our results are shown this way:
  contains articles with the word college but not university or information.
  contains articles with the word university but not college or information
  contains articles with the words college and university but not information
contains articles with the all three of the search terms - these are the articles I want to look at closely
contains articles with the word information but not college or university

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Boolean Searching on the Internet
When you use an Internet search engine, the use of Boolean logic may be manifested in three distinct ways:
Full Boolean logic with the use of the logical operators
Implied Boolean logic with keyword searching
Predetermined language in a user fill-in template

Full Boolean logic with the use of the logical operators

Many search engines offer the option to do full Boolean searching requiring the use of the Boolean logical operators.
Examples:  (search results displayed in gray)
Query:    I need information about cats. Query:    I'm interested in dyslexia in adults.

Boolean logic:    OR

Search:    cats OR felines

Boolean logic:    AND

Search:    dyslexia AND adults
Query:    I'm interested in radiation, but not nuclear radiation. Query:    I want to learn about cat behavior.

Boolean logic:    NOT

Search:    radiation NOT nuclear

Boolean logic:    OR, AND

Search:    (cats OR felines) AND behavior

 
Note: Use of parentheses in this search is known as forcing the order of processing. In this case, we surround the OR words with parentheses so that the search engine will first process this part of the search. Next, the search engine with combine this result with the last part of the search. Using this method, we are assured that the OR terms are kept together as a logical unit.

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 Implied Boolean logic with keyword searching

Keyword searching refers to a search type in which you enter terms representing the concepts you wish to retrieve. Boolean operators are not used.
Implied Boolean logic refers to a search in which symbols are used to represent Boolean logical operators. In this type of search on the Internet, the absence of a symbol is also significant, as the space between keywords defaults to either OR logic or AND logic. Many well-known search engines, such as AltaVista (main screen), Excite, Infoseek, and MetaCrawler, default to OR.
Implied Boolean logic has become so common in Web searching that it may be considered a de facto standard.
Examples:  (search results displayed in gray)
Query:    I need information about cats. Query:    I'm interested in dyslexia in adults.

Boolean logic:    OR

Search:    cats  felines

Boolean logic:    AND

Search:    +dyslexia  +adults
Query:    I'm interested in radiation, but not nuclear radiation. Query:    I want to learn about cat behavior.

Boolean logic:    NOT

Search:    radiation  - nuclear

Boolean logic:    OR, AND

Search:    cats  felines +behavior

 

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Quick Comparison Chart:
Full Boolean vs. Implied Boolean vs. Templates
  Full Boolean Implied Boolean Template Terminology
OR college or university college    university
*see note below		 any of these words
can contain the words
should contain the words
AND poverty and crime +poverty    +crime all of these words
must contain the words
NOT cats not dogs cats    -dogs must not contain the words
should not contain the words
NEAR, etc. cats near dogs N/A near
* This search statement will resolve to AND logic at certain engines including AOL.COM Search, Google, Lycos and Northern Light because the implied Boolean logic at these engines defaults to AND. Be sure to consult the Help files at each search engine site find out which logic is the default.
Where to Search:
A Selected List
Feature Search Engine
Boolean operators AltaVista Advanced Search | C4 | Dogpile | Excite | HotBot | HotBot SuperSearch | Ixquick Metasearch | Lycos Pro | Northern Light | ProFusion | Snap Power Search | WebCrawler
Full Boolean logic with parentheses, e.g.,
behavior and (cats or felines)		 AltaVista Advanced Search | C4 | Excite | HotBot | HotBot SuperSearch | Ixquick Metasearch | Lycos Pro | MSN Search Advanced Search | Northern Light | Snap Power Search
Implied Boolean +/- Most search engines offer this option
Boolean logic by template terminology AltaVista Power Search | AOL.COM Search Options | Excite Power Search | FAST Search Advanced Search | Fossick | GO.com Power Search | HotBot | HotBot SuperSearch | Infoseek Advanced Search | Lycos Pro | MetaBug | MSN Search Advanced Search | SavvySearch | Snap Power Search | Snoopa
Proximity operators AltaVista Advanced Search | Google [by default] | Ixquick Metasearch

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