What are Boolean Search Statements?
 

In computer searching, Boolean search statements are used to narrow or expand a search by linking search terms with the connectors AND, OR, or NOT.  These Boolean operators define how the searches are performed. 
 
Boolean search ORSample search: solar energy 
 
If  solar energy is the search statement, the search engine retrieves Internet resources that have the word solar and puts them in Set A.  It also retrieves Internet resources that have the word energy and puts them in Set B.  The search result is both sets. 
 
This is the same as searching for solar OR energy 
 Boolean search AND 
 
 
 

If solar AND energy is the search statement, the search engine retrieves Internet resources that have the word solar and puts them in Set A.  It also retrieves Internet resources that have the word energy and puts them in Set B.  Then, it compares the two sets and delivers a list of Internet resources that have both terms. 
 
 
 
 
 
 
Combining ORs and ANDs 
The English language is rich in synonyms -- different words to express the same, or similar, ideas. Computers just look for what you tell them to look for.  If the best Web resource in the world on your topic does not use the term you first thought of but, rather, a synonym for it, you would miss that resource unless you also searched for the synonym. 

Put searches for synonyms as OR statements in parentheses.  This tells the computer to amalgamate those terms into one set.  For example, since power and energy are synonyms, and solar and sun are as well, I might use this search statement: 

    (solar OR sun) AND (power OR energy)
The search retrieves Web pages that used phrases such as "using the sun as an energy resource...;"   "the power of solar radiation..." 
 

Eliminating terms with AND NOT 
Systems employing solar energy can be either passive or active.  If I were, for example, interested only in active solar energy systems, I could try a focused search such as this: 

    (solar OR sun) AND (power OR energy) AND NOT passive 
    Boolean search AND NOT
 
Phrases can be used in Boolean search statements, as in the following examples: 
    ("solar energy" OR "solar power") AND efficiencies 
    "solar heat" AND "conversion systems" 
 
The search engines are not precise in how they search, retrieve, and rank results, but, in general, Boolean search statements afford you the most precision and control.  Practice, patience, and persistance pay off!  Since Internet resources usually link to similar or related sites, you are often able to explore valuable resources after having disovered a fairly small number of highly relevant beginning resources.  It's discovering those initial sites that's the challenge.  ; -) 


Who was George Boole? 
 
George BooleGeorge Boole (1815-1864) was an English mathematician.  His An Investigation into the Laws of Thought, on Which are founded the Mathematical Theories of Logic and Probabilities (published in 1854) approached logic in a new way by reducing it to a simple algebra, incorporating logic into mathematics. It began the algebra of logic called Boolean algebra which now finds application in computer construction, switching circuits, and online searching. 
 
 
 
 
 
 
 
 
 
 

T. N. Smalley  7/99; last rev. 1/04