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Summary of discussion on GRDDL and OWL/XML from GRDDL comment list

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Wed, 21 May 2008 11:31:11 +0100
Message-ID: <4833F9EF.2000900@ibiblio.org>
To: Jeremy Carroll <jjc@hpl.hp.com>, public-owl-comments@w3.org


    After a brief revival (See [1] for full discussion) , it appears 
that discussion brought up by Bijan over the relationship between OWL2 
XML and GRDDL has come to some sort of end - so I'll summarize what I 
think the message to the OWL2 WG over this debate is from the remaining 
active members of the GRDDL WG on this list. Note that the GRDDL WG is 
officially no longer active and this message is a personal summary of an 
individual, not an official WG response.

   In effect, while it appears active GRDDL WG members on the list  
recognize the dangers posed by someone thinking an conformant GRDDL 
transformation in XSLT for OWL2/XML to RDF is more "normative" than some 
other transformation, it appears to be the feeling of the majority of 
the remaining active people from the GRDDL Working Group that the 
benefits of having such a GRDDL transformation accessible from the 
namespace document of OWL2's XML syntax outweigh the costs.

This is in particular  *if* the OWL2 Working Group believes that 
RDF-aware agents may want to access information in OWL2 in RDF and may 
not have their own locally installed OWL2 XML to RDF transformer.

So:

   1) It seems general opinion in the GRDDL WG that having a GRDDL 
Transformation Property point to a non-executable list of 
implementations is not a useful use of GRDDL, and the GRDDL WG did not 
explicitly discuss this possibility when creating the GRDDL 
Specification or test-cases. A GRDDL transformation, while not 
necessarily XSLT, is usually executable, and currently all examples are 
in XSLT.

   2) However, while the "cost" of alienating developers of other 
non-GRDDL transformations may exist, this is a misunderstanding about 
the "normative" nature of GRDDL transformations. In particular, a list 
of other conformant implementations could be accessible at the namespace 
document using RDDL [2]. Also, a few sentences explaining GRDDL and the 
fact that it is no more "normative" than other implementations could be 
included in the namespace document. If this does actually cause 
problems, these problems could be dealt with re the usual feedback 
channels of the W3C. The advantage of having a GRDDL from OWL/XML to RDF 
is that it is that a particular audience (RDF users without an explicit 
OWL 2 to RDF transform), who might otherwise be unable to have what 
benefits the OWL 2 in RDF, can have these benefits with a minimal of work.

   3) Having a GRDDL transform does not prevent clients from using other 
local transformers instead if they are preferred. As for the possibility 
of the OWL namespace document being overloaded by requests for the 
transform, we do in the specification encourage caching of GRDDL 
transformations. Regards the possibility of GRDDL transformations being 
"automatically" run, this is a matter of local policy determined 
explicitly by the user. Current libraries such as Redland and Jena do 
allow GRDDL to be turned on explicitly by the local client.

   Although this is not the solution that Bijan wants per se, think this 
is the general opinion of the GRDDL WG members who have responded so far 
on this list. Thanks to Bijan for the provocative and intelligent 
critiques and comments re GRDDL and OWL 2.

   The choice of whether or not to include a GRDDL transformation that 
is an XSLT from OWL2 XML to RDF is, of course, in the competent hands of 
the OWL 2 WG. However, I do hope this feedback helps clarify things.

         -harry

[1] http://lists.w3.org/Archives/Public/public-grddl-comments/2008AprJun/
[2]http://www.rddl.org/
Received on Wednesday, 21 May 2008 10:31:56 GMT

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