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by Susan Ives |
It's happened to all of us. You're searching for something on the World Wide Web and get a million hits. Or no hits at all. Or bunches of weird hits that have nothing at all to do with your interests. How do you structure a search to get back the information you need? There are more than 250 search engines on the Internet. Most of them use a symbolic logic system called Boolean Logic, named after George Boole, the mathematician who invented it. It uses a set of connecting words - AND, OR, NOT and NEAR - to make your search more precise. Let's try it. Your daughter needs help with her fourth grade science project about pythons.
You search for the keyword python and get 135,264 hits, most of them about the Monty Python's Flying Circus television show. What next?
You decide to use two terms to narrow your search. You type the keywords python snake and get twice as many hits as before. What went wrong? 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 the site about Texas, for example, you might want to use the keyword 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 both words must 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 instead of the AND operator; "python-snake" has the same effect as python AND snake. Another variation is to use a semi-colon as in 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".
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 narrow your search. In this example, you could also have typed +python -monty.
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 keywords 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 located somewhere within the same document. Let's 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 keywords appear in the document. To limit your hits to a reasonable number, 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, snakes and pythons, 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.
All of the search engines have their own peculiarities. I recommend that you pick one or two, learn them inside out and upside down and stick with them. The more proficient you get at structuring your searches, the more successful you will be.
Susan Ives is co-chair of the Alamo PC Internet SIGs. She has not taken a math course since she squeaked by with a B in 10th grade trigonometry but still manages to use Boolean Logic. Reprint from PC Alamode, The News Magazine of the Alamo PC Organization, Inc.
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