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RE: [ALL] RDF/A Primer Version

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Fri, 3 Feb 2006 23:57:52 -0500
Message-ID: <A5EEF5A4F0F0FD4DBA33093A0B075590097B6820@tayexc18.americas.cpqcorp.net>
To: "Ben Adida" <ben@mit.edu>
Cc: "Dan Connolly" <connolly@w3.org>, "Jeremy Carroll" <jjc@hpl.hp.com>, "Miles, AJ (Alistair)" <A.J.Miles@rl.ac.uk>, "SWBPD list" <public-swbp-wg@w3.org>, "public-rdf-in-xhtml task force" <public-rdf-in-xhtml-tf@w3.org>, "Pat Hayes" <phayes@ihmc.us>

Cut to the chase: My best guess at this point is that the practice of
having http://www.w3.org/People/Connolly/#me identify both a location
within a document *and* a foaf:Person is NOT actually in conflict with
the WebArch, although the WebArch is confusing in this area.  Full
explanation below.

> From: Ben Adida [mailto:ben@mit.edu] 
> . . .
> Now I'm very confused.
> 
> I thought we were discussing whether a resource that *might* be an  
> HTML document *could* also be a non-information resource, say a  
> person.  Let's take a precise example.
> 
> DanC's FOAF Person URI is <http://www.w3.org/People/Connolly/#me>,  
> but <http://www.w3.org/People/Connolly/> returns HTML, which makes  
> <http://www.w3.org/People/Connolly/#me> a (potential) HTML element.

The httpRange-14 decision says that if an HTTP GET of
http://www.w3.org/People/Connolly/ returns a 2xx status, then
http://www.w3.org/People/Connolly/ is an "information resource".

The WebArch says that the meaning of the fragment identifier ("#me") is
determined by the media type that is returned.  In the case of HTML, it
identifies a location with the HTML document.  Therefore, according to
the WebArch plus the httpRange-14 decision,
http://www.w3.org/People/Connolly/#me identifies a location within an
HTML document.  

If Dan is also using http://www.w3.org/People/Connolly/#me to identify a
foaf:Person, then the same URI is being used both to identify a
foaf:Person and an "information resource".  Is this okay?  Pat Hayes
does not see this as a problem, as he has eloquently explained.
However, the WebArch says that a URI should only identify one resource,
so my issue was this behavior seemed inconsistent with the WebArch.  

On the other hand, the WebArch also says that if multiple media types
are served using content negotiation, then because the meaning of the
fragment identifier could differ for different media types, the URI
owner should ensure that all such meanings are "sufficiently
consistent"[1] (and hence conceptually would still only identify a
single resource).  The WebArch also says that "The representation
provider decides when definitions of fragment identifier semantics are
are sufficiently consistent".

Is it reasonable to think that the use of
http://www.w3.org/People/Connolly/#me as a location within a document
would be "sufficiently consistent" with its use as a foaf:Person?  I
would not have thought so, since, to me, a document seems very different
from a person.  In fact, I could well imagine the class of
tag:Location-Within-An-HTML-Document as being owl:disjointWith
foaf:Person.

However, as Jeremy pointed out, there clearly is an intentional
relationship between them: the location within the HTML document
provides a human-readable description of the same foaf:Person.  I.e., in
some sense, a coercion is possible between them.  If this is the kind of
"consistency" that the TAG intended, then my concern about this practice
conflicting with the WebArch is unfounded.  Also, I just ran across some
of TimBL's earlier thoughts[2] on the TAG's RDFinXHTML-35 issue[3], and
they give further evidence that this *is* the kind of "consistency" that
the TAG intended.

So my best guess at this point is that the practice of having
http://www.w3.org/People/Connolly/#me identify both a location within a
document *and* a foaf:Person is NOT actually in conflict with the
WebArch, although the WebArch is confusing in this area.

> 
> DBooth, I thought you were saying that this is probably a bad thing,  
> assuming HTMLElement subclasses InformationResource, etc...
> 
> Did I misunderstand?

Answered above.

> 
> If DanC's setup is okay by the TAG, then I *think* that means that a  
> secondary resource can be a non-information resource, even when its  
> primary resource is an information resource. Someone correct me if  
> I've lost it.

That is definitely true.  I don't think the debate was ever about that.
However, it depends on the *media* *type* that is returned -- not merely
on the fact that the primary resource is an information resource.

Ben, thanks for all your work on this.  It's a very nice primer.

David Booth

[1] WebArch on fragment identifiers and content negotiation:
http://www.w3.org/TR/webarch/#frag-coneg

[2] TimBL thoughts on RDF in HTML:
http://www.w3.org/2002/04/htmlrdf

[3] TAG issue RDFinXHTML-35:
http://www.w3.org/2001/tag/issues.html#RDFinXHTML-35

[4] RDF/A Primer:
http://www.w3.org/2001/sw/BestPractices/HTML/2006-01-24-rdfa-primer

[5] Alistair's issues on URI usage in RDF/A primer:
http://lists.w3.org/Archives/Public/public-swbp-wg/2006Jan/0113.html
Received on Saturday, 4 February 2006 04:58:02 UTC

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