I have added XFN annotations to my blogroll; you notice the new logo to the right:

XFN (short for XHTML Friends Network) is a really simple way to annotate hyperlinks with information about personal relationships. It took me all of five minutes to add it with no tools support whatsoever.

For example, if want to say that Alan Steele a friend and a coworker, I just add the attribute rel=”friend coworker” to the hyperlink to his blog:

< a rel="friend coworker" href="http://www.drizzle.com/~asteele/blog.html">Alan Steele < /a >

Search engines are already starting to crawl this information and provide more meaningful relationship based results. For example, there is a search engine called Rubhub that has indexed these relationships:

See my relationships on Rubhub

Rubhub is a very basic version of what could be quite a powerful relationship map built on top of hyperlink annotations.

From here, you can imagine a virtuous cycle [1] of increased usage, search engine and web services support, better tools, and a more sophisticated relationship schema. Eventually stronger notions of identity, signing and trust will be possible on the open internet in a way never before possible.

The social network would span the open internet instead of being a walled garden and expose itself as a web services platform on top of which interesting applications could be built.

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[1] You could tell the same “virtuous cycle” story with FOAF or many other technologies. The critical point is that the initial standard has to be so simple and easy that an interested core of people can do quick and dirty adoption without tools, as was the case with the the web itself.