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Re: Generic processing of Fragment IDs in RFC 3023bis

From: Graham Klyne <GK-lists@ninebynine.org>
Date: Thu, 07 Oct 2010 12:52:00 +0100
Message-ID: <4CADB460.8050208@ninebynine.org>
To: "Martin J. Dürst" <duerst@it.aoyama.ac.jp>
CC: Jonathan Rees <jar@creativecommons.org>, "Roy T. Fielding" <fielding@gbiv.com>, Noah Mendelsohn <nrm@arcanedomain.com>, Norman Walsh <ndw@nwalsh.com>, www-tag@w3.org
Martin J. Dürst wrote:
> Given that XML fragment identifiers are pretty well established these 
> days, it would in my opinion be a rather strange failure on the RDF side 
> to create an RDF-based vocabulary to identify XML elements (and other 
> syntactic constructs) where the same fragment id identifies different 
> XML elements.

I think the difficulty here is not that RDF uses fragment identifiers to 
identify some different XML element than other XML formats, but that RDF uses 
fragment identifiers in a way that is largely orthogonal to the XML structure.

(The RDF abstract syntax is independent of XML or any other specific 
serialization format, and uses URIs with - or without - fragment identifiers to 
name arbitrary concepts.  RDF does not know about XML so is silent on the matter 
of what XML element might be identified by a fragment.  RDF/XML, the specific 
serialization of RDF in XML, does not add materially to RDF's treatment of URI 
fragments.  Further, RDF/XML does not itself specify any interpretation of 
xml:Id attributes.)

[1] http://www.w3.org/TR/rdf-concepts/

[2] http://www.w3.org/TR/REC-rdf-syntax/

>> Without considering the question of which library the application
>> "should" use, it appears that you are saying three things: first, that
>> this is a perfectly natural state of affairs, so it has to be accepted
>> because it's the way the world works;
> 
> I'd say that the RDF side should be fixed.

I'm not sure there's anything to be fixed.  A generic XML handling application 
that processes fragment identifiers to select some part of an RDF/XML document 
doesn't break anything in RDF, but may produce a result that is not obviously 
related to RDF's interpretation of the full URI reference as a name.

If generic XML applications are used with RDF/XML, and apply some standard XML 
interpretation of fragment identifiers, I don't see that causing any meaningful 
breakage.

>> second, that the cat is out of
>> the bag and we couldn't change things even if we wanted to;
> 
> Is there already such an RDF library?

Just about every bit of RDF code out there treats URIs-with-fragment identifiers 
as names, without reference to the structure of any corresponding RDF/XML.  But 
AFAIK there is no RDF library that specifically attempts to interpret fragment 
identifiers with respect to the structure of some RDF/XML document.

...

In summary, I think the situation outlined by Normal Walsh [3], as supported and 
expanded by Roy Fielding [4] generally holds as described for RDF.  I.e. that if 
applications fail, it will be "less badly".

The particular scenario suggested by Roy would, I think, be entirely harmless. 
Even if a fragment-as-XML-view coincides with a fragment-as-part-of-RDF-name 
use, neither use would be distorted by the existence of the other.

[3] http://lists.w3.org/Archives/Public/www-tag/2010Oct/0006.html

[4] http://lists.w3.org/Archives/Public/www-tag/2010Oct/0012.html

#g
Received on Thursday, 7 October 2010 11:53:59 GMT

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