A search engine is a program that searches for documents on the Internet using keywords and that returns a list of the requested documents. In this particular context, the term search engine is used to refer to programs such as Google, Yahoo!, and Alexa which enable users to search for documents on the World Wide Web. Search engines use algorithms. There are three different types of search engines:
- Search engines with so-called "robots" which search for new websites through links: Google, Yahoo!, Alexa, exalead
- Meta-search_engines which don't have any database of its own, but which automatically requests the same query at several external online search engines: ixquick, dogpile, SurfWax
- Specific search engines with or without its own database searching for specific informations(news-spider.com, picsearch.com, PeekYou), displaying results in an unique way(Clusty, Quintura, Kartoo) or converting/adding queries intelligently(hakia, accoona, ChaCha)
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the first search engine was introduced in January 1993.