As an online merchant, you want your Web site listed at the top of search engine results so customers can find you. But in order for this to be effective, you need to understand how search engines use algorithms to index and rank sites. Search engines can be distinguished from directories by how they work. Search engines, including Google, Excite and AltaVista, send out applications called spiders to scan the Web pages submitted to them and store the URLs and associated keywords. Search engines recursively retrieve all pages linked from this first set of pages, harvesting more and more links.
Some search engines have larger site indexes to draw from, and some update their indexes more often.
The result is that no single search engine has the same collection of Web pages in its index. Also affecting your site's search results is each search engine's ranking algorithm , the complex mathematical proportion used to determine a site's relevancy. Directories rarely use such algorithms, as relevancy is often determined by the editor's opinion of the site. Each algorithm assigns weights to factors that include keywords , page title, emphasized text, description meta tags , URL and site popularity. Site popularity is measured by the number of links to the page .