more keywords can help you narrow down your results and get very
specific pages, but you have to be careful because many simple
search engines may not interpret those three words, or the relationships
between them, as you might want. When using three or more keywords
it is often best to use engine that will allow you to use Boolean
logic operators to define the relationship between the words.
narrow down your results and to get more specific you can add more
words. Two or more keywords separated by the Boolean operator AND
(all three letters capitalized) will tell the search engine that
every keyword must be on the page.
The Boolean logic expression canoe AND
kayak will ensure that the engine uses both
words in its search and ranking logic and that both words
appear on the pages returned.
you want to broaden your search to find documents which contain
either of the keywords, use the OR
operator between words. This is very useful when searching for
a term which has a synonym that might be used in a document instead.
An example is lesson OR tutorial,
which would return any document which had either of the words.
Using the capitalized AND NOT preceding
a search term would eliminate documents which contain that term.
Why might you want to do this? If you want to find information
on Dieon Sanders and do not want documents that include information
relating to the Dallas Cowboys you could use "Dieon
Sanders" AND NOT cowboys
operator is a more specific form of the AND operator. It ensures
that the document contains both terms and that they are located
near each other (within a certain number of words). In many lengthy
documents, just using the operator AND might not provide useful
results as the two keywords might be located in very different parts
of the document and might not be related to one another.
The expression resistance NEAR antibiotic
used in Alta Vista's advance search engine will ensure that the
engine uses both words in its search and ranking logic
and that both words appear within 10 words of each other
on the pages returned.
The operators AND, NEAR, OR and AND NOT are powerful in their own
right but when used in conjunction with parentheses, they can offer
substantial control over the search logic executed by the engine.
Parentheses are used in Boolean logic similar to the way they are
used in a mathematical equation, limiting and ordering relationships
between variables. The most common use of parentheses is to enclose
two possible keywords separated by an OR
operator and then linking those enclosed/possible keywords with
other keyword using AND.
Here's an example: If you want to find a web-based internet tutorial
you might use the search criteria internet
AND (tutorial OR lesson). The documents returned must
contain both of the words internet
and tutorial or.... internet
and lesson. Essentially, the parentheses
are used to distribute the keyword internet
to either of the two "OR" words inside the parentheses.
If you did not use the parenthesis and used the expression internet
AND tutorial OR lesson the
word internet would only have
to be present on a page with the word tutorial.
A page with just the word lesson
would be returned as well.
Using the OR operator outside parentheseis
does not distribute the word outside parenthesis to words inside.
Example - internet OR (tutorial OR lesson)
will not ensure pages have internet
and either tutorial or lesson.
The search in this case could yield pages that have any one of
the three keywords.
NOTE: The phrase internet OR (tutorial
lesson) is essentially the same as internet
OR tutorial AND lesson. All documents would have to
have internet or..... tutorial
Each left side parenthesis must be paired with a right side one
somewhere in the Boolean expression or the search engine will
get confused (see how stupid they are!). If you make this kind
of mistake many engines will return the message "syntax error"