Canonical URL's - the end of duplicate content issues?
Google, Yahoo and Microsoft have announced support of a format to help prevent the notorious duplicate content problem. With the inclusion of a new header tag in the HTML code of pages that are accessible through multiple URL's you can tell search engines which URL is the preferred, 'canonical' version.
Duplicate content issues have been around for a long time and are hard to eliminate. Especially for database-driven sites that use query elements or session ID's in the URL, it's often the case that a single webpage can be accessed through various different URL's. Other sites may link to the same content on your website with different URL's, thus diluting link value and page rank for that content.
The new feature announced yesterday by the big three search engines provides a simple, elegant solution to this persistent problem. Now all a webmaster has to do is include a <link> tag in the header of the page's HTML code that specifies which URL is the canonical URL, and the search engines will update their indexes to reflect this. Google even claims the page rank of the duplicate URL's will be transferred to the canonical URL.
Hopefully this will spell the end of on-site duplicate content issues. More information about the exact use of the <link> tag can be found in the Google Webmaster Central blog post.
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