The Internet is a vast computer database, or a network of networks. Since there is such a vast array of information stored in various methods, it is often difficult to find what you are looking for. 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.

Boolean logic consists of three logical operators:

OR

AND

NOT

Query:    I would like information about college.

• In this search, we will retrieve records in which AT LEAST ONE of the search terms is present. OR logic is most commonly used to search for synonymous terms or concepts.

Here is an example of how OR logic works:

The more terms or concepts we combine in a search with OR logic, the more records we will retrieve.

For example:

• Notice how we do not retrieve any records with only "poverty" or only "crime"

Here is an example of how AND logic works:

The more terms or concepts we combine in a search with AND logic, the less records we will retrieve.

For example:

A few Internet search engines make use of the proximity operator NEAR. A proximity operator determines the closeness of terms within a source document. NEAR is a restrictive AND. The closeness of the search terms is determined by the particular search engine. For example:

• NEAR in AltaVista (Power Search) is 10 words
• NEAR in Lycos (Lycos Pro) is 25 words

Query:    I want to see information about cats, but I want to avoid seeing anything about dogs.

• In this search, we retrieve records in which ONLY ONE of the terms is present
  
  
• This is illustrated by the shaded area with the word cats representing all the records containing the word "cats"
  
  
• No records are retrieved in which the word "dogs" appears, even if the word "cats" appears there too

Here is an example of how NOT logic works:

NOT logic excludes records from your search results. Be careful when you use NOT: the term you do want may be present in an important way in documents that also contain the word you wish to avoid.

Boolean Searching on the Internet

When you use an Internet search engine, the use of Boolean logic may be manifested in three distinct ways:

1. Full Boolean logic with the use of the logical operators

   Implied Boolean logic with keyword searching

   Predetermined language in a user fill-in template

1. 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:

Boolean logic:    OR

Search:    cats OR felines

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Query:    I'm interested in dyslexia in adults.

Boolean logic:    AND

Search:    dyslexia AND adults

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Query:    I'm interested in radiation, but not nuclear radiation.

Boolean logic:    NOT

Search:    radiation NOT nuclear Query:    I want to learn about cat behavior.

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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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2. 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. Most well-known search engines, with the exception of Lycos and Northern Light, default to OR.

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Examples:

Query:    I need information about cats.

Boolean logic:    OR

Search:    cats    felines

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Query:    I'm interested in dyslexia in adults.

Boolean logic:    AND

Search:    +dyslexia    +adults

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Query:    I'm interested in radiation, but not nuclear radiation.

Boolean logic:    NOT

Search:    radiation    -nuclear

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Query:    I want to learn about cat behavior.

Boolean logic:    OR, AND

Search:    cats    felines    +behavior

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3. Predetermined language in a user fill-in template

Some search engines offer a search template which allows the user to choose the Boolean operator from a menu. Often the logical operator is expressed with substitute language rather than with the operator itself.

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Query:    I need information about cats

Boolean logic:    OR

Search:    Any of these words/Can contain the words/Should contain the words

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Query:    I'm interested in dyslexia in adults.

Boolean logic:    AND

Search:    All of these words/Must contain the words

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Query:    I'm interested in radiation, but not nuclear radiation.

Boolean logic:    NOT

Search:    Must not contain the words/Should not contain the words

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Query:    I want to learn about cat behavior.

Boolean logic:    OR, AND

Search:    Combine options as above if the template allows multiple search statements

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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 can contain the words or 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 Lycos and Northern Light because the implied Boolean logic at these engines defaults to AND.

Where to Search

Feature	Search Engine
Boolean operators	AltaVista (Advanced Search) Cyber411 Dogpile Excite HotBot HotBot SuperSearch NetFind Northern Light WebCrawler
Full Boolean logic with parentheses e.g., behavior and (cats or felines)	AltaVista (Advanced Search) Cyber411 Excite HotBot HotBot SuperSearch Lycos Pro MSN Web Search Advanced Search Northern Light WebCrawler
Implied Boolean +/-	AltaVista Chubba Excite HotBot HotBot SuperSearch Infoseek Lycos Lycos Pro Mamma MetaCrawler NetFind Northern Light Northern Light Power Search PlanetSearch
Boolean logic By Predetermined Language	Excite (Power Search) HotBot HotBot SuperSearch HuskySearch Infoseek Advanced Search Lycos Pro SavvySearch
"Near"	AltaVista (Advanced Search) Cyber411 Dogpile Lycos Pro WebCrawler