What Information Have the Engines Provided About the Canonical URL Tag?

Google:

Is rel="canonical" a hint or a directive?
It's a hint that we honor strongly. We'll take your preference into account, in conjunction with other signals, when calculating the most relevant page to display in search results.


Can I use a relative path to specify the canonical, such as ?
Yes, relative paths are recognized as expected with the tag. Also, if you include a link in your document, relative paths will resolve according to the base URL.

Is it okay if the canonical is not an exact duplicate of the content?
We allow slight differences, e.g., in the sort order of a table of products. We also recognize that we may crawl the canonical and the duplicate pages at different points in time, so we may occasionally see different versions of your content. All of that is okay with us.


What if the rel="canonical" returns a 404?
We'll continue to index your content and use a heuristic to find a canonical, but we recommend that you specify existent URLs as canonicals.

What if the rel="canonical" hasn't yet been indexed?
Like all public content on the web, we strive to discover and crawl a designated canonical URL quickly. As soon as we index it, we'll immediately reconsider the rel="canonical" hint.

Can rel="canonical" be a redirect?
Yes, you can specify a URL that redirects as a canonical URL. Google will then process the redirect as usual and try to index it.


What if I have contradictory rel="canonical" designations?
Our algorithm is lenient: We can follow canonical chains, but we strongly recommend that you update links to point to a single canonical page to ensure optimal canonicalization results.



Yahoo!:

The URL paths in the tag can be absolute or relative, though we recommend using absolute paths to avoid any chance of errors.

A tag can only point to a canonical URL form within the same domain and not across domains. For example, a tag on http://test.example.com can point to a URL on http://www.example.com but not on http://yahoo.com or any other domain.

The 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.

We will use the tag information as provided, but we’ll also use algorithmic mechanisms to avoid situations where we think the tag was not used as intended. For example, if the canonical form is non-existent, returns an error or a 404, or if the content on the source and target was substantially distinct and unique, the canonical link may be considered erroneous and deferred.

The tag is transitive. That is, if URL A marks B as canonical, and B marks C as canonical, we’ll treat C as canonical for both A and B, though we will break infinite chains and other issues.


Live/MSN:

This tag will be interpreted as a hint by Live Search, not as a command. We'll evaluate this in the context of all the other information we know about the website and try and make the best determination of the canonical URL. This will help us handle any potential implementation errors or abuse of this tag.

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. For example, if the page is found on “http://mysite.com/default.aspx”, and the ”href” attribute in the link tag points to “http://mysite2.com”, the tag will be invalid and ignored.
o However, the “href” attribute can point to a different subdomain. For example, if the page is found on “http://mysite.com/default.aspx” and the “href” attribute in the link tag points to “http://www.mysite.com”, the tag will be considered valid.

Live Search expects to implement support for this feature sometime in the near future.

SEO is a part of SEM (Search Engine Marketing) or Online Marketing

If you are getting started to do SEO for you site or blog, here is some tips on what not to do. Search engine spiders are intelligent than you. In other words they are more intelligent than what you think about them.

Cross Linking It’s okay to link your sites together. People do it all the time. However, it can be considered spam if you do so excessively (e.g., in the footer or side bar of every page), especially if the sites reside on the same IP block. As with everything else, ask the question, “Is this adding value for the user?” If you can answer yes, it’s probably okay.

Mirrored Sites and Content Duplication “Never settle for one top 10 rankings when you can have all ten?” This might be the thought when you start SEO. This may cause all of your rankings to drop. Your content should be as unique as possible to a single page. Search engines are probably smart enough to recognize content duplication within blogs (e.g., the same post text on your home page and the individual post page). Generally speaking, though, the more unique your content is, the better off you’ll be.

Keyword Stuffing This will not going to help you in any way. Moreover stuffing keywords may help your site get penalized or delisted. Search engines are very good at detecting this. Whether you’re putting them in your content, in alt tags, in meta tags, or wherever, be sure to use your keywords in moderation.

Cloaking Showing one thing to users and another thing to search engine spiders is a big red flag. It’s just as easy for a spider to change its user agent as it is for a browser. You can bet search engine spiders are crawling your site under a variety of names just to see if you’re cloaking or not, so don’t do it.

Hidden Text and Images As I told earlier search engine crawlers are smarter than you think. It is easy for them to detect the hidden stuffs. Granted, there are legitimate reasons to hide content from users, but it’s pretty obvious when you’re up to something.

Finally, while doing SEO just keep in mind that the results will not come overnight. It will take months.

If you don’t have enough patience spend some bucks and try PPC.