Boolean Searching on the Internet

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

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.

Boolean logic consists of three logical operators:

Each operator can be visually described by using Venn diagrams, as shown below.

college OR university 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.
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.

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

AND

poverty AND crime Query: 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"

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

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 (Advanced Search) is 25 words

NOT

cats NOT dogs 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

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:

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:

Query: I need information about cats.

Boolean logic: OR
Search: cats OR felines

Query: I'm interested in dyslexia in adults.

Boolean logic: AND
Search: dyslexia AND adults

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.

Boolean logic: OR, ANDSearch: (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.

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.

Examples:

Query: I need information about cats.

Boolean logic: OR
Search: cats felines

Query: I'm interested in dyslexia in adults.

Boolean logic: AND
Search: +dyslexia +adults

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

Boolean logic: NOT
Search: radiation -nuclear

Query: I want to learn about cat behavior.

Boolean logic: OR, ANDSearch: cats felines +behavior

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.

Query: I need information about cats

Boolean logic: OR
Search: Any of these words/Can contain the words/Should contain the words

Query: I'm interested in dyslexia in adults.

Boolean logic: AND
Search: All of these words/Must contain the words

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

Boolean logic: NOT
Search: Must not contain the words/Should not contain the words

Query: I want to learn about cat behavior.

Boolean logic: OR, AND
Search: Combine options as above if the template allows multiple search statements

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 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
Implied Boolean +/-	AltaVista Excite HotBot HotBot SuperSearch Infoseek Lycos Lycos Pro Mamma MetaCrawler NetFind Northern Light PlanetSearch
Boolean logic by template terminology	Excite (Power Search) HotBot HotBot SuperSearch HuskySearch Infoseek Advanced Search Lycos Pro SavvySearch
Proximity operators	AltaVista (Advanced Search) Cyber411 Dogpile Lycos Pro WebCrawler

Laura Cohen | June 1998
lcohen@cnsvax.albany.edu

Boolean Searching on the Internet

A Primer in Boolean Logic

Boolean Searching on the Internet

Quick Comparison Chart: Full Boolean vs. Implied Boolean vs. Templates

Where to Search

Quick Comparison Chart:
Full Boolean vs. Implied Boolean vs. Templates