May 18, 2009

“Canonical” solution to search engine woes

Search engines

The top search engines have collectively agreed on a solution to a problem that has long vexed web developers and web site owners.

Google, MSN, and Yahoo have announced support for the use of a “canonical” link tag as part of a page’s markup to help identify duplicate content. The three have a combined search market share of over 90 percent, according to several independent rating surveys.

Search engines analyze web site content by programmatically crawling through each page. In an effort to provide better search results to consumers, the search engines will penalize a site for having duplicate content. However, if multiple different links such as:

http://www.example.com/Category/Item/12345
http://www.example.com/Item?id=12345
http://www.example.com/Item/some-item

…result in the same or similar content, then the site may be penalized by the search engine even though there may be a valid reason for this condition.

Now developers can use a link tag such as:

<link rel=”canonical” href=”http://www.example.com/Category/Item/12345″ />

…on each of the duplicate results to alert the search engine that even though there may be the same content on several pages on the site, that the separate results are canonical to a single point on the site and should be treated as such.

This development is important to web professionals in that resources previously used to combat an erroneous duplicate content penalty can be shifted elsewhere.

Proper use of this new technique is one more tool for use in creating better search engine marketing results.

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