rel- Microformats

Description

While XFN is used to identify social relationships between linked web pages, the rel attribute is also used to indicate specific (non-social) relationships between the source of the link and the destination page via "rel-nofollow", "rel-license" and "rel-tag".

Example

Here’s an example of rel-license, indicating that the link destination is a license agreement:

Photos on this page are subject to a <a rel="license"
href="http://creativecommons.org/licenses/by-nc-sa-2.5/">Creative
Commons license (non-commercial)</a>.

nofollow

Many search engines see the creation of a link from one page to another as indicating some form of approval. You’ve probably heard of Google’s use of PageRank—just one of the measures Google has to calculate a web page’s worth. When a page that has a high Page Rank links to another resource, some of that rank is passed on to the destination page. Thus, an industry has grown up around that simple mechanism whereby spammers try to profit from the system by creating numerous links to their own web pages in the hope that this will result in more page rank being passed on to their sites, giving them better search result placings. It’s for this reason that guest books, blog comments, and forums can be inundated with automated submissions that include spam links.

The "nofollow" Microformat arose as a result of this problem. Placing "nofollow" inside the rel attribute informs the various search engines that the link is not endorsed by the author, and should not be indexed, nor be given any credit in terms of Page Rank (or a similar ranking algorithm). It’s now included by default in many blog comment systems where commenters are asked to provide their URLs. So if I were to try to submit a comment to a Wordpress-powered blog, and provided a URL of a cheap airfares web site with the phrase “cheap flight,” that information would appear in the source markup as follows:

Comment by <a rel="nofollow"
href="http://super-cheap-flights.com/flights/cheap/discounts/">Cheap
Flights</a>

This would not provide any benefit in terms of the search engines—it would only be useful to people who viewed the site and chose to click on the link.

license

If you want to indicate your policy regarding copyright and use or the re-use of your content to people browsing your site, you can link to a page that contains all the relevant licensing information—for example, to a page on the Creative Commons web site. However, you could go one step further by adding rel="license" to the link, as shown below:

Photos on this page are subject to <a rel="license"
href="http://creativecommons.org/licenses/by-nc-sa-2.5/">Creative
Commons license (non-commercial)</a>.

This provides extra information about your content—information that’s machine-readable and could be used for the purposes of filtering search results. For example, you can search for content that has been published under such licenses at http://search.yahoo.com/cc. The return of appropriate search results is made possible by web page authors who use the rel="license" Microformat in their links.

tag

Tag-based navigation is a concept whose usage has grown massively thanks to the support provided to it in blogging systems. In case you’re not familiar with tagging (and it should be noted that when I say tags, I’m talking about something different than HTML opening and closing tags), it’s basically the process of categorizing content. So, for example, if you post an article on your blog about the trials and tribulations of keeping your old car running, you might tag it as "car", "repairs", "tutorial", and "Volkswagen". You could then use these tags to navigate to category index pages that include all posts that have been tagged as "car", "tutorial", and so on.

The rel-tag Microformat provides a way to indicate that the page that’s linked to is a category parent page for the current page, the content of the tag identified by the link phrase. Take a look at this example:

<p>This article is filed under <a href="/tags/car/"
rel="tag">car</a>, <a href="/tags/repairs/"
rel="tag">repairs</a></p>

This is a very, very simple Microformat, and it’s probably one that you don’t need to concern yourself with unless you’re in the process of creating your own Content Management System or blogging tool. Otherwise, you’ll find that most blogging systems already add this Microformat for you.

User-contributed notes

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