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"Search engine" and "Web directory" are two different search services
available to the Web community; although they are often mistakenly
confused. Search engines have indices that are built up by robots or
crawlers; whereas Web directories build up their indices through human
editors. Many search engines and directories contain both a
computer-generated index and a human generated index, and are referred to
as hybrids.
Google, Inktomi, AltaVista, AlltheWeb and the like are all forms of search
engines. These search engines write programs known as robots, crawlers
and/or spiders that have the following functions: (1) to locate Web pages,
(2) to read the contents of the Web pages and (3) report its findings back
to the search engine's indices or databases. Many search engines update
their index either on a bi-monthly or monthly basis. When Web searchers
use a search engine to locate Web sites that are relevant to the keyword
search, they are searching the search engine's index. A search engine with
a larger and more up-to-date index is a better representation of the
information available in the Web.
Yahoo!, Open Directory Project (dmoz.org), Gipsy and the like are all
forms of Web directories. These directories use human editors to review
sites that are submitted for submission to the directory. Directories,
unlike search engines, use a hierarchical tree structure to organize their
database. Another common distinction is that a directory tends to list Web
sites (root directory of a site or homepage) whereas a search engine will
list Web pages (individual pages of a Web site). Due to the manual process
of adding sites to a directory, directories often have to supplement their
search results with a search engine partner to increase the relevancy of
the produced search results.
Search engines all have their own confidential algorithms that determine
which Web pages are to be shown first. The algorithms assign weights to
certain components or variables that it finds within a page.
Web directories should be browsed through their hierarchical structure and
not searched. Humans assign titles and descriptions that might not be
within the source code of the page. Also, there is normally a submission
fee to be added to a directory.
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