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Hybrid engines. Meta Search Engines.
Hybrid engines.
Some engines also have an integrated directory linking to them. They contain websites that have already been discussed or evaluated. When sending a search query to a hybrid engine, the sites already evaluated are usually not scanned for matches; the user has to explicitly select them. Whether a site is added to an engine’s directory generally depends on a mixture of luck and content quality. Sometimes you may “apply” for a discussion of your website, but there’s no guarantee that it will be done.
Yahoo (www.yahoo.com) and Google (www.google.com), although mentioned here as examples of a directory and crawler respectively, are in fact hybrid engines, as are nowadays most major search machines. As a rule, a hybrid search engine will favor one type of listing over another. For example, Yahoo is more likely to present human-powered listings, while Google prefers its crawled listings.
Another approach to searching the vast Internet is the use of a multi-engine search, or meta-search engine that combines results from a number of search engines at the same time and lays them out in a formatted result page. A common or natural language request is translated to multiple search engines, each directed to find the information the searcher requested. The search engine‘s responses thus obtained are gathered into a single result list. This search type allows the user to cover a great deal of material in a very efficient way, retaining some tolerance for imprecise search questions or keywords.
Examples of multi-engines are MetaCrawler (http://www.metacrawler.com) and DogPile (http://www.dogpile.com). MetaCrawler refers your search to seven of the most popular search engines (including AltaVista and Lycos), then compiles and ranks the results for you.
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