FOAF vs. XFN

Well, that title is a bit misleading perhaps. I have been looking at the foaf thingie in the edit form for a user's
account. What this thing does, basically, is to grab the information from your profile, and your buddy list and create a
foaf file out of it. The first question is what, exactly, is a foaf file?

I have been only vaguely aware of FOAF(Friend Of A Friend) having seen it around before but have never really looked at it closely.
From the FOAF Project [1] page:

The Friend of a Friend (FOAF) project is about creating a Web of machine-readable homepages describing people, the links between them and the things they create and do.

Okay, that's easy enough to understand. So the next question is what good is it? For what is it used?

Again, the FOAF Project page to the rescue. There is a link labeled FAQ on the site, which in reality is a link to aIBM's [2] site and an article [3] by
Edd Dumbill [4]. Here is what Edd says about the potential
of FOAF:

FOAF has the potential to become an important tool in managing communities.
In addition to providing simple directory services, you could use information from FOAF in many ways. For example:

• Augment e-mail filtering by prioritizing mails from trusted colleagues
• Provide assistance to new entrants in a community
• Locate people with interests similar to yours

The concept of FOAF becomes very interesting when thinking in context of "social networking". For a while, "social networks" were all the rage. But they were closed systems, that in order to join required an "invitation" to somebody already subscribed to that network. The development of an /xml/rdf vocabulary that is open and free allows you do implement similar concepts but under your control and not limited to any specific "social network". The article [3] is well worth the read if you are interested in this type of thing.

However, being a wide reader of various blogs, and having implemented Wordpress [5] for some
acquaintances, I am also aware of XFN, or XHTML Friends Network [6]. From that page:

XFN™ (XHTML Friends Network) is a simple way to represent human relationships using hyperlinks. In recent years, blogs [7] and blogrolls [8] have become the fastest growing area of the Web. XFN enables web authors to indicate their relationship(s) to the people in their blogrolls simply by adding a 'rel' attribute to their <a href> tags, e.g.:

<a href="http://jeff.example.org" rel="friend met">...

There is a little more detailed introduction here [9]. So what are the differences? Not
really sure, but there is a page on the XFN site just on that topic: http://gmpg.org/xfn/and/foaf [10].
And here [11] is a short critique of XFN over at O'Reilly Network [12].

I should note that RealNEO [13] supports FOAF, but not as far as I can tell XFN. So perhaps its not worth worrying about.