Hint at Duplicate Content with Canonical Value

The three major search engines: Live, Yahoo and Google have agreed to adopt a new standard to highlight URLs that contain duplicate content. Duplicate content issues often occur when the same pages of content is accessed can be reached by multiple URLs or session IDs, particularly common in e-commerce sites, for example, where the same product might exist in different categories. There was always a concern that this could result in duplicate content penalties.

The new attribute value is ‘canonical’ is used with the rel attribute in the links tag. It specifies the location of the page that this is a duplicate of. For example, This page is the same for the URLs:

To tell the search engines that this is duplicate content,  you would have to insert

into the head section of the page of http://www.example.com/product.php?item=swedish-fish&category=gummy-candy (of course for a dynamic site this will require some additional scripting.) Pluggins are already available for WordPress , Magento and Drupal.

More information on this subject can be found on the search engine’s blog pages: Live Search, Google , Yahoo

The instruction acts like a 301 redirect so that PageRank from a particular page that is marked as being duplicate content will transfer its PageRank from that page to the one specified in the canonical link. It will also work at the sub-domain level but not across different domains so this will eliminate the risk of PageRank hijacking.

Specifying the canonical attribute value in a page does not guarantee that it will be considered as duplicate content but it will be strongely considered according to all the search engines. This is surely a welcome piece of cooperation for both webmasters and search engines alike.