[uf-discuss] Re: A (big) problem with XFN: identity of source andtarget not findable

Toby A Inkster mail at tobyinkster.co.uk
Tue Mar 18 09:26:20 PST 2008

Costello, Roger L. wrote:

> How do you know that the hCard matches to the XFN, particularly if the
> XFN is not embedded within the hCard?

Effectively, this:

	<span class="vcard">
	  <a class="fn url" href="http://bob.example.com">Bob Jones</a>

says "Bob Jones" has the URL "http://bob.example.com". And this:

	<a rel="friend" href="http://bob.example.com">Bob</a>

says that "http://bob.example.com" is the URL for a friend. So it can be 
inferred that Bob Jones is a friend.

Of course, Bob Jone's hCard might link to, say, his workplace's website -- 
indeed several hCards could link to the same workplace website. So then it 
becomes more difficult to understand what rel="friend" means when it links 
to that same website. Are they *all* friends?

A better solution would be to the hCard's "uid" property to indicate that 
one particular URL acts as an identifier for one particular hCard. Then an 
XFN link to that same URL could unambiguously describe a relationship to 
that person.

I don't know how widespread the use of "uid" is in practise though. My own 
parser (Cognition) will make up its own UID in the case where none exists, 
as its internal data model requires a unique identifier (which must 
conform to IRI syntax) for every object being described.

Toby A Inkster BSc (Hons) ARCS
[Geek of HTML/SQL/Perl/PHP/Python/Apache/Linux]
[OS: Linux, up 18:52.]

                              The Semantic Web

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