Re: schemaMapping issues breakdown (issue 6)

Hi all,

We worked on this issue when we were writing the WSDL-S spec. I agree with
Jacek's comments (especially option 1c). Comments are inline.

Hi all,
>
> here's an attempt to break down what I think are the separate issues in
>
> clarifying schemaMapping (issue 6 [1]). This email is written with my
> chair hat off. 8-)
>
> I assume that schemaMapping attribute points to a document that
>
> specifies a transformation. It seems that there are two orthogonal sets
>
> of options that we need to consider. Wherever I use RDF below I mean any
> ontological data language (can be RDF, WSML or any such language of
>
> choice).
>
> 1) The transformation is a) between an XML Schema on one side and an
>
> ontology on the other side (schema-level mapping) or b) between XML
> document conforming to the XML Schema on one side and RDF data that uses
>
> some ontology on the other side (data-level, runtime mapping).
>
> I believe option a) above is not useful because the XML Schema in WSDL
> is given and static, the transformation is as static, so the result is
>
> also static, and therefore it can be saved somewhere and pointed to
> using modelReference, as opposed to requiring the processor to take the
> schema, run the transformation, and arrive at the same result every
> time.
>
> herefore I assume 1b for the formulation and discussion of the
>
>
> following aspect:
>
> 2) The transformation goes a) from XML to RDF, b) from RDF to XML, or
> c) both ways.
>
> Since I dismissed the option 1a above, schemaMapping cannot be used
> easily for discovery, instead it could be used when a service is
>
>
> discovered to work with the necessary semantic terms, and then the
> client that has instances of those terms wants to invoke the service so
> it has to transform between its semantic data and the XML that the
>
> service requires.
>
>
> I believe that we need to consider both directions because the service
> both consumes and produces XML messages, so messages for the service
> have to be created from semantic data, and messages from the service
>
>
> need to be parsed back into semantic data.
>
> Depending on whether SAWSDL wants to enable invocation or only discovery
> (and composition, which uses similar data), we may keep or drop
> schemaMapping, and if we keep it, we may need to talk about which
>
>
> directions of the mapping it should handle.
>
> The conclusion is that we have to decide whether we want schema-level
> mapping and whether we want data-level mapping, then what directions for
> the mapping(s) we want to handle. (I'd say "no, yes, both".)
>
>
I totally agree with this and I think that modelReference is sufficient if
providing a semantic match is the only concern. SchemaMapping becomes
important only during invocation, when the heterogeneties between the XML
data and the OWL instances have to be considered. Hence, I think that option
1c) makes the most sense.


We have been working on the issue of providing mapping both ways. We call it
upcast (XML to ontological language) and downcast (ontological language to
XML).  I would like to share this paper that discusses some of the
heterogeneity that may arise and discusses as scenario that uses upcast and
downcast.

Meenakshi Nagarajan, Kunal Verma, Amit P. Sheth, John A. Miller, Jonathan
Lathem, Semantic Interoperability of Web Services - Challenges and
Experiences, Proceedings of the 4th IEEE Intl. Conference on Web Services,
Chicago, IL, September 2006 (to appear).
http://lsdis.cs.uga.edu/library/download/techRep2-15-06.pdf

Thanks,
Kunal

-- 
Kunal Verma,
LSDIS Lab, Dept. of Computer Science,
University of Georgia.
URI: http://lsdis.cs.uga.edu/~kunal <http://lsdis.cs.uga.edu/%7Ekunal>