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salam every one, this is a topic from google web master centrale blog:
Carpe diem on any duplicate content worries: we now support a format that allows you to publicly specify your preferred version of a URL. If your site has identical or vastly similar content that's accessible through multiple URLs, this format provides you with more control over the URL returned in search results. It also helps to make sure that properties such as link popularity are consolidated to your preferred version.

Let's take our old example of a site selling Swedish fish. Imagine that your preferred version of the URL and its content looks like this:

http://www.example.com/product.php?item=swedish-fish


However, users (and Googlebot) can access Swedish fish through multiple (not as simple) URLs. Even if the key information on these URLs is the same as your preferred version, they may show slight content variations due to things like sort parameters or category navigation:

http://www.example.com/product.php?item=swedish-fish&category=gummy-candy

Or they have completely identical content, but with different URLs due to things such as a tracking parameters or a session ID:

http://www.example.com/product.php?item=swedish-fish&trackingid=1234&sessionid=5678

Now, you can simply add this <link> tag to specify your preferred version:

<link rel="canonical" href="http://www.example.com/product.php?item=swedish-fish" />

inside the <head> section of the duplicate content URLs:

http://www.example.com/product.php?item=swedish-fish&category=gummy-candy
http://www.example.com/product.php?item=swedish-fish&trackingid=1234&sessionid=5678

and Google will understand that the duplicates all refer to the canonical URL: http://www.example.com/product.php?item=swedish-fish. Additional URL properties, like PageRank and related signals, are transferred as well.

This standard can be adopted by any search engine when crawling and indexing your site.

Of course you may have more questions. Joachim Kupke, an engineer from our Indexing Team, is here to provide us with the answers:

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 <link rel="canonical" href="product.php?item=swedish-fish" />?
Yes, relative paths are recognized as expected with the <link> tag. Also, if you include a <base> 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.

Can this link tag be used to suggest a canonical URL on a completely different domain?
**Update on 12/17/2009: The answer is yes! We now support a cross-domain rel="canonical" link element.**

Previous answer below:
No. To migrate to a completely different domain, permanent (301) redirects are more appropriate. Google currently will take canonicalization suggestions into account across subdomains (or within a domain), but not across domains. So site owners can suggest www.example.com vs. example.com vs. help.example.com, but not example.com vs. example-widgets.com.

Sounds great—can I see a live example?
Yes, wikia.com helped us as a trusted tester. For example, you'll notice that the source code on the URL http://starwars.wikia.com/wiki/Nelvana_Limited specifies its rel="canonical" as: http://starwars.wikia.com/wiki/Nelvana.

The two URLs are nearly identical to each other, except that Nelvana_Limited, the first URL, contains a brief message near its heading. It's a good example of using this feature. With rel="canonical", properties of the two URLs are consolidated in our index and search results display wikia.com's intended version.

Feel free to ask additional questions in our comments below. And if you're unable to implement a canonical designation link, no worries; we'll still do our best to select a preferred version of your duplicate content URLs, and transfer linking properties, just as we did before.

Update: this link-tag is currently also supported by Ask.com, Microsoft Live Search and Yahoo!.

Update: for more information, please see our Help Center articles on canonicalization and rel=canonical.

Written by Joachim Kupke, Senior Software Engineer, and Maile Ohye, Developer Programs Tech Lead
this is a topic published in 2013... to get contents for your blog or your forum, just contact me at: devnasser@gmail.com

from web contents: Specify your canonical 2013

salam every one, this is a topic from google web master centrale blog:

Note: The SEO Starter Guide has since been updated.

Webmasters often ask us at conferences or in the Webmaster Help Group, "What are some simple ways that I can improve my website's performance in Google?" There are lots of possible answers to this question, and a wealth of search engine optimization information on the web, so much that it can be intimidating for newer webmasters or those unfamiliar with the topic. We thought it'd be useful to create a compact guide that lists some best practices that teams within Google and external webmasters alike can follow that could improve their sites' crawlability and indexing.

Our Search Engine Optimization Starter Guide covers around a dozen common areas that webmasters might consider optimizing. We felt that these areas (like improving title and description meta tags, URL structure, site navigation, content creation, anchor text, and more) would apply to webmasters of all experience levels and sites of all sizes and types. Throughout the guide, we also worked in many illustrations, pitfalls to avoid, and links to other resources that help expand our explanation of the topics. We plan on updating the guide at regular intervals with new optimization suggestions and to keep the technical advice current.

So, the next time we get the question, "I'm new to SEO, how do I improve my site?", we can say, "Well, here's a list of best practices that we use inside Google that you might want to check out."

Update on July 22, 2009: The SEO Starter Guide is now available in 40 languages!
Written by Brandon Falls, Search Quality Team
this is a topic published in 2013... to get contents for your blog or your forum, just contact me at: devnasser@gmail.com

from web contents: Google's SEO Starter Guide 2013

salam every one, this is a topic from google web master centrale blog: At Google, we are always working hard to provide searchers with the best possible results. We've found that our spam reporting form is a great way to get your input as we continue to improve our results. Some of you have asked for a way to report paid links as well.

Links are an important signal in our PageRank calculations, as they tend to indicate when someone has found a page useful. Links that are purchased are great for advertising and traffic purposes, but aren't useful for PageRank calculations. Buying or selling links to manipulate results and deceive search engines violates our guidelines.

Today, in response to your request, we're providing a paid links reporting form within Webmaster Tools. To use the form, simply log in and provide information on the sites buying and selling links for purposes of search engine manipulation. We'll review each report we get and use this feedback to improve our algorithms and improve our search results. in some cases we may also take individual action on sites.

If you are selling links for advertising purposes, there are many ways you can designate this, including:
  • Adding a rel="nofollow" attribute to the href tag
  • Redirecting the links to an intermediate page that is blocked from search engines with a robots.txt file
We value your input and look forward to continuing to improve our great partnership with you.this is a topic published in 2013... to get contents for your blog or your forum, just contact me at: devnasser@gmail.com

from web contents: More ways for you to give us input 2013

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