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

Ryan King ryan at theryanking.com
Wed Mar 19 16:11:58 PST 2008

This is not a big problem, its mostly solved with [1]


1. http://microformats.org/wiki/representative-hcard

On Mar 18, 2008, at 5:31 AM, Costello, Roger L. wrote:

> Hi Folks,
> Flickr uses XFN.  Here is a sample Flickr page that uses XFN:
> http://www.flickr.com/people/tantek/
> At the browser menu select View >> Page Source.  Then search for rel=
> Here's an example usage of XFN within that Flickr page:
> <a href="/photos/24172116 at N08/" rel="contact">
>    <img
> src="http://farm3.static.flickr.com/2146/buddyicons/24172116@N08.jpg? 
> 12
> 03935044#24172116 at N08"
>         alt="Jolene_A" width="48" height="48" /><br />
>    Jolene_A
> </a>
> Notice the use of XFN: >>> rel="contact" <<<
> Metafilter also uses XFN.  Here is a sample page that uses XFN:
> http://www.metafilter.com/usercontacts/292
> Here's an example usage of XFN within that page:
> <a href="/user/10411" rel="colleague" target="_self">40 Watt</a>
> Notice the use of XFN: >>> rel="colleague" <<<
> Now, suppose that I wanted to create a spider application which crawls
> all social networks that use XFN.  Most likely, I would want the  
> spider
> to collect:
> 1. Who is the source?  That is, who is the individual using XFN to
> state a relationship?
> 2. What is the relationship?  This is, of course, obtained easily from
> the value of the rel attribute on the link.
> 3. Who is the target?  That is, who is the other individual in the
> relationship?
> Examine the above snippets of code.  Does 1. and 3. pop out at you?
> That is, do you know who are the individuals that are the source and
> target of the relationship?
> That information "can" be found on the Flickr and Metafilter sites,  
> but
> each site does it *differently*.
> So, the problem with XFN can be stated as this: While XFN does a great
> job of providing a set of relationship values (friend, contact,
> co-worker, etc), it provides no means for the automated discovery of
> the individuals that are the source and target of the relationship.
> Without information about the source and target individuals, the
> relationship information is not very useful.
> You might argue: "Well, the XFN *should* be embedded within an hCard,
> then you can discover who the source individual is.  And the target
> page should contain an hCard, then you can discover who the target
> individual is."  And I agree that is Best Practice.  Unfortunately,
> this is not mandated and consequently many people don't do it.  For
> example, Flickr and Metafilter don't do it.  Nor do any of the other
> social networks do it.
> Conversely, consider FOAF.  Advogato is a social network that uses
> FOAF.  Here an example FOAF on that network:
> http://www.advogato.org/person/connolly/foaf.rdf
> At the browser menu select View >> Page Source to see the actual FOAF
> document.  Notice that the individual who is the source of the
> relationship is clearly listed at the top of the document:
> <foaf:name>Dan Connolly</foaf:name>
> And the individual who is the target of the relationship is clearly
> identified:
>    <foaf:knows>
>      <foaf:Person
> rdf:about="http://www.advogato.org/person/jtauber/foaf.rdf#me">
>        <foaf:nick>jtauber</foaf:nick>
>        <rdfs:seeAlso
> rdf:resource="http://www.advogato.org/person/jtauber/foaf.rdf"/>
>      </foaf:Person>
>    </foaf:knows>
> The downside of FOAF is the only built-in relationship is "knows",  
> e.g.
> "Dan Connolly knows James Tauber." That is, FOAF doesn't possess the
> richness of expression in terms of relationships. (I know, there are
> extensions of FOAF to express more than "knows," but as far as I can
> tell, no social network is using those extensions)
> The upside of FOAF is that all three pieces of information are
> available to a spider application:
> 1. The source individual (e.g. Dan Connolly)
> 2. The relationship ("knows")
> 3. The target individual (e.g. James Tauber)
> I don't see any solution to the problem with XFN.  As far as I can  
> see,
> social networks using XFN cannot be processed by spiders.  Only social
> networks that use FOAF can be processed by spiders.  Bummer.
> Hopefully, I am missing something.  I really like the simplicity of  
> and its rich set of relationships.
> /Roger
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