Back to Contents pageThe basic distinction between a search engine and a subject directory is that in a search engine the user enters search terms in a form which seeks results from computer-generated indexes, whereas in a directory generally the user follows a human-compiled hierarchies. In practice things are slightly more complicated as many search engine services are trying to become portals and have selective directories of recommended sites, and subject directories often have search facilities. The best guide to these is Danny Sullivan's regularly updated Search Engine Watch. This site contains discussions of different types of subject search facilities on the Internet, factual information on how search engines work, and details of the features of individual services.
Services which maintain large databases of Websites, compiled by robots supplemented by manual submission, which are searched using IR software. Usually produce ranked output. The extent of facility to use Boolean etc operators varies; Ian Winship has a comparative table of Web search service features.
The main problem with search engines is their tendency to overload the user with hundreds of allegedly relevant results, in spite of covering a decreasing proportion of available sites (See Size of the Web, Web Size, Search Engine Coverage and Recency by Steve Lawrence and Lee Giles of the NEC Research Institute). Some knowledge of search strategies is useful - otherwise the best results are obtained when searching for names of organisation etc, especially where these contain unusual words.
Services giving the facility to search more than one search engine by entering search terms in a single form. Sites with multiple forms which have to be completed individually are listed under Lists of, and guides to, search engines, below.
Manually classified lists of Websites using either a scheme of nested menus or an existing classification scheme, usually with a search facility.
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Page created by Martin Nail. Copyright © 2004 Martin Nail. Last revised 18th April 2004