Search Engines Summary

Search engines have three major elements. First is the spider, also called the crawler. The spider visits a web page, reads it, and then follows links to other pages within the site. The spider returns to the site on a regular basis, such as every month or two, to look for changes.

Everything the spider finds goes into the second part of a search engine, the index. The index, sometimes called the catalogue, is like a giant book containing a copy of every web page that the spider finds. If a web page changes, the index is automatically up-dated but there may be a time lag of several weeks between "spidering" and indexing.

Search engine software is the third part of a search engine. This is the program that sifts through the millions of pages recorded in the index to find matches to a search phrase and rank them in order of what it believes is most relevant. The quality of the match determines where a site will be placed in the rankings.