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Re: XML Schema draft populates the intersection of Language and InformationResource [ISSUE-14 httpRange-14]

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sat, 29 Sep 2007 00:45:49 +0200
Message-Id: <70FC68E8-FEFC-43FE-ABDC-85066BC7CC2C@cyganiak.de>
Cc: www-tag@w3.org
To: "Chimezie Ogbuji" <chimezie@gmail.com>

Chimezie,

On 28 Sep 2007, at 23:05, Chimezie Ogbuji wrote:

> On 9/28/07, Richard Cyganiak <richard@cyganiak.de> wrote:
>>> Well, I'm not sure it follows that it 'clearly' identifies a section
>>> in the HTML case - unless you are using the web-arch notion of
>>> 'identifies' and not denotation but even so...
>>
>> *Of course* I'm using the web-arch notion of "identifies".
>
> Okay then, you are comparing apples to oranges.  Saying RDF
> 'identifies' things is an abuse of notation as far as I'm concerned.

The terms “denote”, “identify”, “indicate” and “mean” are used  
interchangeably throughout the RDF specs. It's unfair to blame me for  
this.

The mechanism by which fragment URIs in RDF *identify* (not my choice  
of term) are spelled out quite clearly in section 7 of rdf-concepts [1].

> RDF denotes 'things' (the mechanics for this are very well-defined -
> /TR/rdf-mt ), web-arch "identifies".  These are not equivalent
> mechanisms, or at least their definitions do not correspond. If *we*
> are serious about consistency between 'classic' web architecture and
> the semantic web, we need to fix this disconnect *before* suggesting
> best practices prematurely.

Is there really that much of a disconnect?

URIs are governed by a paper trail of RFCs, starting at RFC 3986 and  
leading through the IANA scheme and media type registries, then  
through the RFCs for the different URI schemes such as http: and urn:  
and tag:, and through a whole bunch of media type registrations, and  
from there it bottoms out at specific data format specs such as those  
for HTML and RDF. Thus, webarch gives us a framework that defines URI- 
space, how the space is managed, what operations we can perform on  
URIs, what they identify, and so on.

That's the framework within which RDF has to operate. In terms of rdf- 
mt, I take this to mean that the denotation of many URIs (those that  
have representations, according to httpRange-14) is fixed by the Web.

There is a school of thought that wants to see URI-space as a blank  
slate for the purposes of RDF, completely disconnected from the role  
of URIs on the Web. Personally, I have trouble seeing the advantage  
of this view. If you want to operate in a universe parallel to the  
Web, then why use URIs in the first place? Why not simply use KIF or CL?

(Although, in defense of the “parallel universe” school, this view is  
legitimized by a passage in rdf-mt [2], which, it appears, directly  
contradicts rdf-concepts [1].)

>> No, you are wrong.
>> RFC 3986 says that the "nature" of <doc#term> is
>> determined by the media type of <doc>, governed by the RFC that has
>> registered that media type. The registration for HTML says that
>> fragments identify parts of the HTML document;
>
> Yes, I gathered this from Dan's follow-up response about the HTML RFC
> being the source of the 'problem'.  Still, the ambiguity you are
> speaking about is between two completely orthogonal mechanisms for
> reference ("identification" versus denotation).
>
> Frankly (and this has been my perpetual theme), if there is serious
> concern about ambiguity, then a language well-equipped to handle
> ambiguity should be used.

I do not believe that such a language can resolve the ambiguity.

Quoting RFC 3986:

“If the primary resource has multiple representations, as is often  
the case for resources whose representation is selected based on  
attributes of the retrieval request (a.k.a., content negotiation),  
then whatever is identified by the fragment should be consistent  
across all of those representations.”

Combining a text/html representation with an application/rdf+xml  
representation makes it hard to achieve this consistency, unless  
additional webarch trickery is used (303).

The ambiguity arises on the webarch level, and can only be resolved  
there.

Yours,
Richard

[1] http://www.w3.org/TR/rdf-concepts/#section-fragID
[2] http://www.w3.org/TR/rdf-mt/#urisandlit


> A vacuous notion of "identification" is
> simply not sufficient.
>
>> the registration for
>> RDF says that fragments can identify things outside of the document.
>> Thus the ambiguity.
>
> See above.
>
>  -- Chimezie
>
Received on Friday, 28 September 2007 22:46:02 UTC

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