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Search engines are computer software programs designed to help users of
the Internet locate information on the World Wide Web. It collects and indexes
Internet resources (web pages, programs, images, etc.
) and provides a keyword search system allowing the user to identify and
retrieve resources. There are many search engines available. Some common
search engines are: Google, Yahoo, MSN, Alta Vista, Lycos, HotBot and others.
A search engine operates, in the
following order: crawling website,
indexing and searching site. Web search engines work by storing information
about a large number of web pages, which they retrieve from the WWW itself.
These pages are retrieved by a web crawler
(spider) - an automated web browser which follows every link it
sees. The contents of each page are then analyzed to determine how it should
be indexed (for
example, words are extracted from the titles, headings, or special fields
called meta tags). Data about web pages is stored in an index database
for use in later queries. When a user comes to the search engine and makes a query, typically by giving
keywords, the
engine looks up the index and provides a listing of bestmatching web pages
according to its criteria, usually with a short summary containing
the document's title and sometimes parts of the text.
The usefulness of a search engine depends on the relevance of the results
it gives back. While there may be millions of websites that include a particular
word or phrase, some pages may be more relevant, popular, or authoritative
than others. How a search engine decides which pages
are the best matches, and what order the results should be shown in, varies
widely from one engine to another.
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