A search engine is really three different programs working together as a unit.
The spider (also called a “crawler” or “bot”) is the tool that actually catalogs your site. It reads all the text, detects links to other pages and follows each one.
A second program indexes all the results returned by the spider. This huge database is sometimes known as a catalog.
The final piece is the program that receives your request (using keywords, phrases or terms), matches these to the data in the catalog, and returns ranked results to you.Â
Search engines include google.com, AltaVista, AlltheWeb and AOL Search. Yahoo! is not a true search engine. It is a directory. In contrast to search engines, Yahoo! relies on humans to review listings and manually create result rankings.
Search engines use a variety of techniques to determine rankings. These include meta tags, keywords, link popularity, reciprocal linking and complex mathematical metrics that would have boggled Einstein’s mind.