|Most search engines use a symbolic logic system called
Boolean Logic, named after George Boole, the mathemetician who invented
it. It uses a set of connecting words -- AND, OR, NOT and NEAR -- to make
your search more useful. In this example, let's assume your daughter is
doing a fourth grade science project on pythons.
You search for the key word python and get 5,000 hits, most of them about the Monty Python Flying Circus television show. What next?
You decide to use two terms to narrow your search. You type the key words python snake but get even more hits than the previous search. What happened? If you use two terms without specifying a Boolean operator, most search engines will interpret it as OR. This means that you will get a list of all web sites that contain the word snake and/or the word python. Instead of limiting your search you have expanded it!
Don't discount OR; it can be useful. If you are searching for sites about Texas, for example, you might want to use the key words texas OR TX to make sure you get both the full word and the abbreviation.
You type the keywords python AND snake. Success! This strategy works by specifying that the words python and snake must both appear in the document for it to show up on your hit list. Some search engines allow you to use quotation marks to link words together with the AND operator. "python snake" has the same effect as python AND snake. Another variation is to use a semi-colon: python;snake. Keep this strategy in mind if you ever search for the city of San Antonio, Texas. If your use the keywords San Antonio Texas, you will get hits for all sites containing any of the three words, including ones for San Francisco and Dallas, Texas. Try san AND antonio AND texas, or "san antonio texas". Yet another variation is +san +antonio +texas.
You type the keywords python NOT monty. This will give
you a hit list of all documents that contain the word python but
will exclude any that also contain the word monty. In some search
engines, you can use the + and - signs to narrows your search. In this
example, you could also have typed
Still not convinced that your search is as good as it could be? Some Monty Python pages could slip the word snake into their text just to confuse people, and the key word search python AND snake would not screen them out. Your search for python NOT monty filtered out the Monty Pythons but left in a bunch of other unrelated pythons, such as the Python Software Company. In a case like this, you can combine Boolean search terms to refine results. Try "python snake" AND NOT monty or +python +snake -monty.
Sometimes you might want to make sure that two words are related to each other in a document, not just in the same document. Lets say you wanted to search for me, Susan Ives. If you searched for susan AND ives you might get documents returned that contain Susan Jones and Fred Ives. This is a legitimate hit because both key words appear in the document. To stand a better chance of getting the document you want, use a proximity search. The keywords susan NEAR ives will ensure that susan appears within 10 words of ives, improving your odds of finding me considerably.
Back to pythons. Your search of python AND snake may miss some hits because it does not count variations of a word. To make sure you also pick up the plurals, you might want to add a wild card character, *. Change your search to python* AND snake*. The keyword reptil* will return reptile, reptiles and reptilian.
Ready to try it out? Here is the search form for Alta Vista. Try limiting a search using Boolean logic.