Re: RDF document?

On Fri, 2005-06-10 at 10:28 +0800, Jeremy Wong wrote:
> ----- Original Message ----- 
> From: "Dan Brickley" <danbri@w3.org>
> To: "Jeremy Wong" <jeremy@miko.hk>
> Cc: "Frank Manola" <fmanola@acm.org>; "Chris Purcell" <cjp39@cam.ac.uk>; 
> <semantic-web@w3.org>
> Sent: Thursday, June 09, 2005 8:54 PM
> Subject: Re: RDF document?
> 
> 
> >
> > On Thu, 2005-06-09 at 09:30 +0800, Jeremy Wong wrote:
> >> Thanks for the correction of the term "document". It is an important 
> >> concept
> >> of RDF.
> >>
> >> Consider the property foaf:workplaceHomepage [1], the domain of this
> >> property is the class foaf:Document. Let's see the example..
> >>
> >> <foaf:Person>
> >>  <foaf:name>Dan Brickley</foaf:name>
> >>  <foaf:workplaceHomepage rdf:resource="http://www.w3.org/"/>
> >> </foaf:Person>
> >>
> >> I always think that this example is misleading. I would prefer to put the
> >> above example in the following way..
> >>
> >> <foaf:Person>
> >> <foaf:name>Dan Brickley</foaf:name>
> >> <foaf:workplaceHomepage
> >> rdf:datatype="http://www.w3.org/2001/XMLSchema#anyURI">http://www.w3.org/</foaf:workplaceHomepage>
> >> </foaf:Person>
> >
> > Thanks for the feedback. I don't see it as misleading at all:
> > foaf:workplaceHomepage is a relationship between a foaf:Person and
> > a foaf:Document that is a homepage of a workplace of that person.
> > This is explained in prose and in RDFS in the FOAF
> > specification. I agree that you could, instead, have defined a similar
> > relationship that holds between a person and a datatype-represented
> > URI that identifies such a homepage. These are different modeling
> > styles, each with their own benefits. For FOAF, we focus on the
> > document,
> > and not its identifier, since it is the document that is of interest,
> > and we
> > can mention the document even if we don't know it's URI.
> 
> It is a design issue. I would say that Literal is a medium to communicate 
> with the end-user. Obviously the property foaf:workplaceHomepage is intended 
> to show the information, http://www.w3.org/ in the example, to the end-user. 

Interesting. I'm in a privileged position here, since I remember my 
intent in the design of the property. Unfortunately it seems that
intent 
wasn't adequately communicated in the documentation! I'll try to fix
that.

The absolute core purposes behind foaf:workplaceHomepage 
(also foaf:schoolHomepage) was not really to convey information about
the 
homepage of the organization. It was to identify. We are trying to take
advantage 
of a fact about the world regarding the uneven market for identifiers:
it is
*much* easier to identify a Web document than it is to identify an 
organization. There is no planet-wide, universally adopted system of 
identifiers that can be used to identify organizations directly. So FOAF
took
an indirect approach. We much be, of course, careful not to confuse the
organization with its homepage. But we can, nevertheless, use the 
identifier of the organization's homepage as a way to identify the
organization.
This is useful, for example, when trying to match people who have the 
same workplaceHomepage, or schoolHomepage. I talk about this a bit more
in 
http://rdfweb.org/mt/foaflog/archives/2003/07/10/12.05.33

The value of foaf:workplaceHomepage can be used in other ways,
including --- yes --- being displayed to end users, probably as a 
hyperlink rather than as an 'in your face URL'. But the main game we're 
playing here is trying to find patterns, conventions and tricks that
allow us
(in a global, loosly coordinated system) to identify the things that
matter
to us. Without waiting for someone to create, deploy and evangelise a 
custom URI scheme for each kind of thing.

The foaf:primaryTopic relationship is another part of FOAF that works
like 
this. You can use it, for example, to relate a document to the thing
that it is 
about. The 'primary' aspect, described using OWL's 'functional
property' 
mechanism, reflects the ida that there can sometimes be just one thing
that
a document is primarily about. In such cases, we can indirectly use the 
identifier of the document (eg. a wikipedia page) when trying to share
and 
merge information about the main topic of that page.

cheers,

Dan

Received on Friday, 10 June 2005 08:33:44 UTC