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Mark It Up!

Quite a crop of languages or extensions to existing languages has popped up lately. Many of these languages are related to content aggregation; others, such as XFN, are used to tag relationships between people and people.

RSS and Atom

RSS, also referred to as Real Simple Syndication or Rich Site Summary, is a term used to describe a number of XML-related aggregation technology versions that grew out of a project at Netscape geared to manage news headlines for portal web sites.

Within a short time, seven RSS formats emerged from different vendors, making it a bit difficult to figure out which is best to use. You may have also heard the term RDF, which is Resource Description Format, a more formal XML language being developed at the W3C. RDF, as with all aggregation technologies, is very concerned with metadata and how to use it to connect people to information, and vice versa.

Based heavily on the concepts within RSS, Atom is an emerging next-generation format for content syndication. Its goal is to provide a more stable standardized platform for aggregation and to offer developers far more choice and flexibility than in RSS.

Fortunately, many weblogging tools generate more than one form of RSS, including Atom, and you can manually create RSS and Atom documents, too.


To learn more about RSS, see Mark Pilgrim's "What is RSS?" article. The RDF specification is available at; and information about Atom, including developer tutorials, is published at


FOAF is the Friend of a Friend project. FOAF is described as an "RDF vocabulary." It's used very much like RSS, and has properties that can be used to describe information about individuals—such as nick, homepage, phone and so on. The ultimate goal with FOAF is locate people with similar interests and help build communities.


Learn more about FOAF at The FOAF Project.


XFN is the acronym for XHTML Friends Network. Developed by Matthew Mullenweg (who also is the developer of the semantic blogging software WordPress) along with standards evangelists Eric Meyer and Tantek Çelik, XFN is conceptually like other aggregation technologies, except it uses HTML vocabulary, not other markup languages.

Mullenweg looks to the simplicity of XFN as one of its most appealing points. "I think there are a couple of really exciting things about XFN," he says. "It leverages higher-level semantics into the HTML everyone already knows. You don't have to learn a new awkward syntax or mess with strange files. It takes what you're already doing, linking, and enriches it semantically."

By adding a number of attribute values to the rel attribute, anyone writing documents in HTML or XHTML can make their links XFN-friendly. Here's an example of a link on one of my site's pages to Biz Stone's web site:

<a href="" title="Go to" 
rel="friend colleague">Biz Stone</a>.

As you can see, I added the rel attribute to the link and also added values that describe our relationship as being friends and colleagues. Beyond simple, but sure to be very effective when blogrolls, specialty search engines, blogging tools, and markup editors begin supporting XFN more explicitly.

The other piece of XFN that Mullenweg points to as having tremendous potential is that XFN is distributed, unlike social networking web sites. "XFN doesn't tie you in to any one place; it connects people across domains, literally," Mullenweg says. "The history of the Web has shown that decentralization is the wave of the future."


Learn all about XFN on the XHTML Friends Network site.

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