Re: GRDDL Going to Last Call: Relevance to SAWSDL

Dear Harry, 
thanks for letting us know about the upcoming GRDDL LC. 

On Tue, 2007-02-06 at 22:05 -0500, Harry Halpin wrote:
>  We believe this technology is related to the SAWSDL WG as a GRDDL can
> be considered a type of function or "process" from XML to RDF, and after
> reading the latest version of SAWSDL I believe there is a definite and
> interesting relationship to SAWSDL [5]. First, according to my reading
> of [5], ""liftingSchemaMapping  and loweringSchemaMapping, that are
> added to XML Schema element declarations, complex type definitions and
> simple type definitions for specifying mappings between semantic data
> and XML." In essence, a GRDDL is a way for a "lifting". However, there
> are three  differences:

I agree, GRDDL is a way of lifting.

> 1) "lifting"  as you define it maps to a "semantic model", which "does
> not rely on any particular semantic modeling language. It only requires
> that the semantic concepts defined in it be identifiable via URI
> references."  In this regard, GRDDL is a subset of "lifting," as it
> defines its output to a RDF graph, a subset of all "semantic models".

Yes, GRDDL could be applied for lifting to RDF.

> 2) GRDDL applies to XML documents in general, including XHTML and XML
> Schema. Insofar as "lifting" as defined in SAWSDL by
> "liftingSchemaMapping" refers to XML Schema, GRDDL is a superset of
> "lifting".

I'm afraid there might be a misunderstanding stemming from our attribute
name - schema mapping - because we point to transformations that
transform data, e.g. XML to RDF, not schemata, e.g. XML Schema to OWL.
Do you think a renaming to something like liftingDataMapping and
loweringDataMapping would help?

> 3) Lastly and most importantly, SAWSDL specifIes a way of specifying the
> mapping that is componentized to the types of the XML Schema, while
> GRDDL currently only operates over the whole XML document, and so cannot
> at this time specify transformations at the level of simple and complex
> XML Schema types.

Our mappings also work on the whole document - only the
liftingSchemaMapping that is on the element declaration or type
definition for the root element of the message gets used.

> I think these observatons require no changes to SAWSDL as the spec
> stands. However, it would be nice to put in a reference to GRDDL, such
> as after the sentence: "Other languages, such as XQuery can also be
> used." "GRDDL (Gleaning Resource Descriptions from Dialects of Language)
> is a way of "lifting" XML documents, including XML Schema, to RDF.
> Transformations created for use by GRDDL can be used as lifting mappings
> for SAWSDL if appropriate."

If I understand it correctly, GRDDL puts links to the mappings in the
data itself, so we would not really have much to point to from the data
schema. We can say that instead of pointers in the WSDL (in the schema),
one could employ pointers in the data itself, but I suspect this
wouldn't fly with Web Services people because it would be repeated
overhead.

So in the end, a link to GRDDL in the SAWSDL spec might not be all that
useful, but perhaps GRDDL might be mentioned in our usage guide.

> In other words, nothing new should be implemented, and the note merely
> notices the relationship and that if someone makes a GRDDL transform for
> an XML Schema to RDF someone can save effort and use the same transform
> if wanted in a SAWSDL. I would also like to add a note about the
> relationship to SAWSDL one of the GRDDL documents.

Since SAWSDL doesn't define any mappings itself, I suspect that GRDDL
could only say something like "instead of linking the mappings in the
data itself, they may be linked from the schema, e.g. using SAWSDL's
liftingSchemaMapping, however, this particular mechanism does not allow
combining multiple mappings."

Does it make sense? 8-)
Best regards,
Jacek

Received on Thursday, 22 February 2007 14:28:32 UTC