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Re: [pedantic-web] Re: The OWL Ontology URI

From: Dan Connolly <connolly@w3.org>
Date: Wed, 12 May 2010 10:31:31 -0500
To: Pat Hayes <phayes@ihmc.us>
Cc: Jonathan Rees <jar@creativecommons.org>, AWWSW TF <public-awwsw@w3.org>
Message-ID: <1273678291.3925.2862.camel@pav>
On Tue, 2010-05-11 at 22:36 -0500, Pat Hayes wrote:
> On May 11, 2010, at 1:01 PM, Dan Connolly wrote:
> 
> > On Mon, 2010-05-10 at 15:25 -0500, Pat Hayes wrote:
> >> Let me give an intuitive case in support of the Nays here. An RDF
> >> graph is a set, which is not the same as a document, for sure. The
> >> *same* graph can be encoded in a variety of different syntactic  
> >> forms.
> >
> > Meanwhile, the same resource can have a variety of representations.
> >
> >> Consider two documents, one in RDF/XML, the other in NTriples,
> >> describing the same graph. If we identify the document with the graph
> >> it describes, then these have to be the same.
> >
> > But if we say that those documents _represent_ the graph,
> > they don't have to be the same.
> 
> Yes, quite. The document is not the graph. No document is ever a graph.
> >
> >> But they aren't the
> >> same. So even if a graph is an information resource (and I agree that
> >> one can make out a case for that position), it certainly isn't the
> >> same information resource as any document (In RDF/XML or NTriples or
> >> any other notation) that represents it syntactically.
> >
> > But it can be represented by them.
> 
> Indeed. But it is distinct from them, is my (only) point.

I thought you were showing an argument that graphs are not
information resources.

> >> So, one ought to
> >> use redirection to refer to it, according to http-range-14.
> >
> > I don't see that this follows.
> 
> Well, according to http-range-14, as I understand it, if a bare URI  
> gives a 200-level response to an HTTP GET, then it (the URI) denotes/ 
> refers to the resource that emits that response. And in these RDF- 
> graph-representations,

yes, so far...

>  this is always the syntactic entity at the  
> other 'end' of the HTTP response.

No. The observable syntactic entity is the representation, not
the denoted resource.

>  (Because these things - the  
> syntactic documents which encode the various syntactic representations  
> of RDF graphs - are fully fledged information resources in their own  
> right, so are refer-to-able by URIs,

yes...

>  and are therefore indeed so  
> referred to by them,

I think you went too far there. Given <http://example/xyz>
if I do a GET on that, you can look at what comes back
as a document/information-resource, but you don't have
any evidence that it is called <http://example/xyz>.
You only know that it _represents_ something called
<http://example/xyz>.


>  if they respond with a 200-coded response.) So,  
> such URIs cannot refer to the graph itself (because, as we have  
> already agreed, the graph is never identical to a document of any  
> kind, ie to any information resource that can return a 200-coded  
> response.)

I find it pretty straightforward to deal with this stuff formally
rather than in prose.

If we take w:representation to be the relationship between
a resource and any of its representations, then we have
this axiom in the case of HTTP:

{
_:m a http:OKResponse;
  http:about ?R;
  mime:body ?BYTES;
  mime:content-type ?TYPE.
} => {
?R w:representation [
  mime:content-type ?TYPE;
  mime:body ?BYTES ].
}

In those terms httpRange-14 is just:

 w:representation rdfs:domain w:InformationResource.

(for more, see my IRW 2006 paper http://www.w3.org/2006/04/irw65/urisym )

As Jonathan observes, this is frustratingly little information.

Oh... actually, I suppose webarch does give us just a little
more information about w:InformationResource:

"Other things, such as cars and dogs (and, if you've printed this document on physical
sheets of paper, the artifact that you are holding in your hand), are resources too.
They are not information resources."

so w:InformationResource is disjoint with cars, dogs, and pieces of paper.

That suggests fairly strongly that it's disjoint with people, but doesn't
say so exactly. How about Graphs? Integers? I don't find any compelling
argument based solely on ratified specs and/or decisions of the TAG.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Wednesday, 12 May 2010 15:31:20 UTC

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