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GRDDL Going to Last Call

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Tue, 06 Feb 2007 21:01:02 -0500
Message-ID: <45C932DE.6030109@ibiblio.org>
To: W3C TAG <www-tag@w3.org>, www-archive@w3.org

I'm Harry Halpin, the Chair of the GRDDL WG [1] which links XML and XHTML(including "microformats") to the Semantic Web in order to facilitate the deployment of the Semantic Web.  

 In order to prevent a "surprise" Last Call, I'd like for the TAG to know  that we are going to go, barring any final comments or problems, to  request move to Last Call on or shortly after Feb 15th for the following three documents:

 1) GRDDL Specification [2]
 2) GRDDL Primer [3]
 3) GRDDL Use Cases [4]
 
 We believe this technology is related to the TAG. In our charter [5] there are three TAG issues which are brought up to be relevant:

1) #RDFinXHTML-35 [6]

GRDDL is clearly one easy-to-use and potentially very powerful way to embed RDF in XHTML and will hopefully allow microformat and XML data to be easily converted to Semantic Web data. It is not the only way, and I would note that it's difference with other ways is that RDFa is a "declarative" way while GRDDL is "procedural." Also, unlike using conneg to host a RDF representation  at the same URI that hosts (X)HTML representations, GRDDL is "client-side". In my opinion, GRDDL also is related to the "lifting mapping" of SAWSDL, although unlike SAWSDL it is specific in its "semantic model" and it works over XML documents, not just XML Schema. GRDDL is a method for putting the reference to a function from XML to RDF to be embedded in the XML document itself to internal to the document itself, while SAWSDL's "lifting" allows one to externally specifiy a this reference. from XML to some "semantic model" such as RDF. SAWSDL also includes a "lowering"from XML to some "semantic model" such as RDF, while this is out of scope for GRDDL. 

2) #fragmentInXML-2 [7]

We agree with the conclusion of the TAG of this issue, and GRDDL uses media-types consistent with WebArch as needed to identify transformation languages:

"In general, the fragment part of a URI may be used to refer to abstractions as well as syntactic fragments of a representation; the media type identifies a specification, which explains the semantics." 


3) #rdfURIMeaning-39[8]

In general, we agree with DanC's message [9] that states:

"Web Architecture works because there's a rough, evolving consensus
that to figure out what a URI refers to, you dereference it.
You can also find out about it from other sources, but if those
other sources disagree with representations of R, there's a bug
somewhere. i.e. it's an anomaly, w.r.t. web architecture"

In particular, we allow people to use the same URI to refer to both RDF and XML/XHTML while serving only a XML/XHTML representation server-side, and thus in my opinion GRDDL is a good example of "self-describing" documents.

  In addition, our work does not attempt to solve issues raised recent discussions regarding the "elaborated infoset" [10],  but we do recognize the issues and provide what we believe is a reasonable stand on them by writing an "informative warning" in [2] (drafted by Murray Maloney, edited by Dan Connolly):

"When an information resource is represented by an XML document, the corresponding XPath data model is somewhat under-determined, depending on, for example, whether an agent elaborates inclusions, parameter entities, fixed and default attributes, or checks digital signatures. Put another way, if an author takes responsibility for the information in an XML document, for what information exactly is the author taking responsibility? And how can the author ensure that a GRDDL transformation is able to meet GRDDL's Faithful Rendition assurance?

This specification is purposely silent on the question of which XML processors are employed by or for GRDDL-aware agents. Whether or not processing of XInclude, XML Validity, XML Schema Validity, XML Signatures or XML Decryption take place is implementation-defined. There is no universal expectation that an XSLT processor will call on such processing before executing a GRDDL transformation. Therefore, it is suggested that GRDDL transformations be written so that they perform all expected pre-processing, including processing of related DTDs, Schemas and namespaces. Such measure can be avoided for documents which do not require such pre-processing to yield an infoset that is faithful. That is, for documents which do not reference XInclude, DTDs, XML Schemas and so on."

Please do take the time to look at our upcoming Last Call documents and provide comments as needed.

 
 [1] http://www.w3.org/2001/sw/grddl-wg/
 [2] http://www.w3.org/2004/01/rdxh/spec
 [3] http://www.w3.org/2001/sw/grddl-wg/doc29/primer.html
 [4] http://www.w3.org/2001/sw/grddl-wg/doc43/scenario-gallery.htm
 [5] http://www.w3.org/2006/07/grddl-charter.html
 [6] http://www.w3.org/2001/tag/issues.html#RDFinXHTML-35
 [7] http://www.w3.org/2001/tag/issues.html#fragmentInXML-2
 [8] http://www.w3.org/2001/tag/issues.html#rdfURIMeaning-39
 [9] http://lists.w3.org/Archives/Member/w3c-semweb-cg/2005Sep/0033
 [10] http://www.w3.org/2001/tag/doc/elabInfoset.html



-- 
		-harry

Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Wednesday, 7 February 2007 02:01:09 GMT

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