Boolean Searching on the Internet

Most library 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.


OR

college OR university

Query:    I would like information about college.

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 17,320,770
university 33,685,205
college OR university 33,702,660

OR logic collates the results to retrieve all the unique records containing one term, the other, or both.

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

For example:

Search terms Results
college 17,320,770
university 33,685,205
college OR university 33,702,660
college OR university OR campus 33,703,082


AND

poverty AND crime

Query:    I'm interested in the relationship between poverty and crime.

Here is an example of how AND logic works:

Search terms Results
poverty 783,447
crime 2,962,165
poverty AND crime 1,677

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

For example:
Search terms Results
poverty 783,447
crime 2,962,165
poverty AND crime 1,677
poverty AND crime AND gender 76

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:


NOT

cats NOT dogs

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

Here is an example of how NOT logic works:

Search terms Results
cats 3,651,252
dogs 4,556,515
cats NOT dogs 81,497

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.

 

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, 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.


Send questions or comments to Dawn Lynn (dlynn@luc.edu)