The leading search engines, Google, Yahoo! and

MSN Live, use crawlers to find the pages for

their algorithmic search results. Pages that

are already linked from another search engine’s

indexed pages do not need to be re-submitted

because they will be found automatically. Some

search engines, notably Yahoo!, operate a paid

directory submission service that guarantee

crawling for either a set fee or cost per

click. Such programs usually guarantee quicker

inclusion in the database, but do not guarantee

any specific ranking within the search results,

just that your site will be indexed.<br>

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Yahoo’s paid inclusion program has drawn much

criticism from both advertisers and

competitors. Two major directories, the Yahoo

Directory and the Open Directory Project both

require manual submission and human editorial

reviews before being accepted. Google offers

Google Webmaster Tools, to which an XML Sitemap

file can be created and submitted for free

online to ensure that all pages are found,

especially pages that aren’t easily

discoverable by automatically following links

between pages, such as dynamic content.<br>

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Search engine crawlers (or robots)&nbsp;take

into account a variety of different factors

when crawling a site. Not every page is added

or indexed by the search engines. Distance of

pages (depth) from the root directory of a site

may also be a factor in whether or not pages

get crawled and indexed.