The document discusses different types of search engines including crawler-based engines like Google that automatically crawl the web, human-powered directories like Yahoo, and social search engines that determine relevance based on user contributions. It also discusses meta-search engines that search multiple engines at once, visual search engines that cluster results, and news search engines specialized for current events. New developments discussed include web 2.0 technologies like social networking and mashups.
![How Search Engines Work ,[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)