Search engines produce different results because of the way they are tuned. Engines such as Exite throw in a popularity formula 2 . Web sites that are visited more often than others rank higher. Other sites use reviews to determine relevancy. Users search by term or view definitions related to specific subjects.
Bots are mechanized software which searches Internet sites for relevant and pertinent content.
After being initialized, they search websites and return ranked listings. They also search search engines. Agents are complex software modules which negotiate with websites in order to collect information, or as mentioned above, crawl over the page. Agents do not necessary learn, but they have instruction sets on what to do if a certain reply or reaction is encountered 4 . Here is a listing of several common search engines.