Directories build their databases on submissions by owners of websites. Sites are evaluated and if they meet the appropriate requirement they are added to the database. Another type of information retrieval site is the - search engine . Search engines maintain dynamic databases which are created and managed by a webcrawler .Webcrawlers are also known as robots or spiders . These programs continually search websites looking for updates to existing sites and new sites going online.
Robots allow a search engine to keep their databases current.
Search or query results with a search engine will include information regarding the number of sites or instances found pertaining to the topic you are seeking. Alta Vista , Excite , and Webcrawler are some of the search engines currently providing online search capability. While search engines provide a starting point for a search, the best search for information will require using more than one search engine or directory to ensure you've done a complete search of material available. These sites run your search through several search engines at the same time. This may not be the most complete search for a topic or subject area, but it does cover more ground, saving time when doing online research.