Monday, January 30, 2006

SEO 101 Refresher Part 2: Canonical Issues

Canonical issues is SEO talk for where more than one URL serves one website's content.

Let’s go over a few definitions to set the stage:

root domain name = separates one entity from another on the web, like how a company name sets apart one company from another. Example: zunch.com

subdomain name = separates different parts of an entity on the web and precedes the root domain name. Example format = subdomain.zunch.com.

What many don’t realize is that since anything before the root domain name (ex: zunch.com) is a subdomain, they don't know that 'www', is in fact, a subdomain. Because many web servers by default answer to 'www.site.com' and 'site.com' many site’s already have a canonical issue. In the past, search engines (Google included) have treated these URLs as two different websites. Uh-oh.

If two different URLs are serving a website's content that means that a website's content and link popularity are being split apart. In Google, some documents from one URL would be filtered out while others would be filtered out from the other. This means your content is split up into two different URLs. We always want to create more content for a website - not separate it!

As if this isn't bad enough, your back links could also be split up. Inevitably some sites would use 'www.site.com' and others would just use 'site.com'. Of course, you don’t want your link popularity split among different URLs as your links are a major ranking factor.

If your site is already serving content on each URL you simply need to use a 301 permanent redirect from one URL to the other. The defacto 'www.site.com' is probably a good choice. So in this case you would setup a 301 permanent redirect from 'site.com' to 'www.site.com'. This is rather simple for most web servers, however I have heard that web servers such as Lotus-Domino can be difficult to deal with and a call to support may be needed.

The search engines are making strides to address canonical issues. In the mean time, a use of a simple 301 permanent redirect can keep the canonical issues from being an issue at all.


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