Having duplicate content has been a long lived problem for people with parameter heavy sites or with multiple versions of the same content scattered across many pages. There has never really been an easy way to highlight your preferred URL when you have scattered and similar content. Over on the Google's webmaster blog, they recently posted instructions on how to use the <link> tag to specify the version you prefer.
How is this useful? Two common scenarios that they mention and that I've personally experienced are the use of tracking parameters and result set ordering parameters.
Let's say you have a product page called black-beans.php, but you have the need to append tracking parameters for some reason. You might end up with black-beans.php?tid=4UZ66?ref=moms_site, black-beans.php?tid=4UX04, etc.. With the <link> tag you can let Google (and any other search engine that adopts this standard) know which should be the 'official' singular version of this content. Here's what your tag would look like: <link rel="canonical" href="http://www.site.fake/black-beans.php" />
site.fake vs www.site.fake?
Historically, you would use .htaccess to 301 redirect one version to the other (typically the site.fake to the www.site.fake). Google claims to honor the canonical <link> tag across sub-domains. Using the <link> method might be the only way some people can solve this issue if they don't have the proper access or environment.
IMHO, this is a really cool new feature!
Thanks for the tips. But, we still affraid to fake something with our site or url link.
Posted by: Sulumits Retsambew | 08/04/2009 at 10:50 PM