The Collective Decisions of Competitors

Analogous to the collective wisdom of the masses that some websites mine for the benefit of users, it is heartening to see competing search engines join hands to make search results and the Web more effective. 

Microsoft Live, Yahoo & Google now allow you to "normalize" urls by picking one "canonical" url so that you link consistently within your site. This feature will help search engines solve complex duplicate content issues and make search results more relevant.

To implement this simply add the following link tag inside the head section of the duplicate content URLs to specify your preferred version of several similar URLs:

<link rel="canonical" href="http://www.example.com/products" />

A few technical details:

• This is a hint, not a directive/mandate/requirement. Search engines choose when to use the suggestion
  
• You can use relative or absolute URLs in the “href” attribute of the link tag.
  
• The page and the URL in the “href” attribute must be on the same domain. 
  
• The pages do not have to be bit-for-bit identical, slight differences are okay.
  
• The link tag will be treated similarly to a 301 redirect, in terms of transferring link references and other effects to the canonical form of the page.
  

Google, Microsoft and Yahoo had earlier agreed on the rel="nofollow" attribute in the anchor tag (to prevent comment spam) and the Sitemap protocol