In-depth analysis of SEO canonical tag detailed

Canonical (authoritative link tag) is the 09, Google,yahoo and Microsoft three seo/seo.html "target=" _blank > Search engine jointly launched a proposal to reduce duplication of content, not an order, That means the tag search engine may not comply. China's largest Chinese search engine Baidu has also supported the canonical tag.

Some search engines have introduced a new attribute of link canonical. A page statement b for authoritative links, b statement C as authoritative page, the search engine will consider C is a and B common preferred authoritative version. At this point the canonical tag played a role of 301 redirect.

First, the use of canonical

To put it simply, you add this code to the header of the HTML file.

<link rel= "canonical" Href= "http://www.example.com/product.php?item=swedish"/> Meaning is that the website's standardized web site should be: http:// Www.example.com/produt.php?item=swidish-fish

The following URLs can be added to the canonical tag:

Http://www.example.com/produt.php?item=swidish-fish&category-candy

http://www.example.com/product.php?item=swedish&trackingid=1234&sedssionid=5687 the normalized URL of these URLs becomes: http:// Www.example.com/produt.php?item=swidish-fish

Canonical label is equivalent to a page of 301 turn, the difference is that the user is not turned, or stay on the original web site, and the search engine will take it as a 301 turn processing, the weight of the page to focus on the label specified in the standardized web site.

Also need to note:

1, the label is just a suggestion or hint, not a directive, he is not like a document that is a command. So the search engine will consider this label to a large extent, but not 100%. The search engine will also consider other circumstances to interpret the normalized web site.

2, the label can use the absolute address, also can use relative address

3, the designated content on the normalized web site, and. Other non-standard URLs that use this label can be different, not necessarily exactly the same.

4, the designated standard URL can be nonexistent page, return 404, can also be not included in the page

Some Web sites because of technical limitations can not do 301 turn, canonical tag is very flexible, do not need any special server components or functions, directly written in the page HTML can be.