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he second kind is the searchable subject index. Yahoo's Directory and Open
Directory Project are good examples. A searchable subject doesn't index every
word of every page, or even index every available page on the Web. Instead,
it tries to list sites. And it doesn't list all the words of a site, but rather just the
name of the site, the URL, and some kind of brief description.
two ty pes of Searches in each Search engine
despite the fact that Yahoo got famous because of its Web site directory (its searchable subject 
index),  it  has  in  recent  years  implemented  a  full-text  search  engine.  and  despite  the  fact  that 
google has had a full-text search engine since 1998, it also offers a searchable subject index via 
its google directory. so both search engines offer full-text and subject index searching. 
i  mention  this  when  people  ask  me  “Which  is  better,  full-text  searching  or  searchable  subject 
indexes?” My answer: neither is better overall. it depends on what you're looking for. 
As you might imagine, there's a big diference between a narrow efective query
in a full-text search engine, and a narrow efective query in a searchable subject
index. he diference revolves around the “pool” of data you're searching.
Let's look, for example, at a Web site about trees that has 100 pages with 100
words on each page. Google will attempt to index that entire site. When
Google inishes, that site will be represented in Google's index by 10,000
words of its content. Compare that to Yahoo's Directory or the Open Direc-
tory Project, which would index the same site with only the Web site's title
and a description. In this case, the Web site about trees would be lucky to
have 100 words representing its content.
Because of how much information about a site is indexed in each kind of
search engine, you have to be careful about what you search for. A search for
something as speciic as “southeastern knotty limbed birch tree” would
be perfect for Google but almost useless in Yahoo's Directory. Meanwhile, a
simple search for “birch trees” could bring you useful results at the Open
Directory, but a deluge of results at Google.
For the most part, you'll deal mostly with full-text search engines, so focus
on generating a concentrated, narrow query.
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