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Lyndon J B Nixon wrote:
> skimming through the OWL spec, and trying to grasp it -- as it is an
> extension of RDF Schema just like DAML+OIL
> it can express constraints upon RDF assertions, but what about XML (not
> RDF) vocabularies?
This generally was a feature called "structured XML datatypes" that didn't
make it (as it currently looks) into the first version of OWL, and will
likely be postponed for a later version of the languages.
I have been the main agitator for including this in OWL, but there are
several (little) problems at present which prevent such features from
actually being tested, implemented etc.
There is a partial solution, for simple datatypes, that I'll discuss below.
It is possible that a general solution can be _built on_ OWL as it stands
today, but someone needs to do that.
> i.e. considering TBLs layers for the Web
> Ontologies e.g. OWL
> Metadata e.g. RDF
> Data e.g. XML
> Can the ontological layer only be built upon the metadata layer? if so,
> how could I state equivalences and other
> relationships between XML elements/attributes? Isn't that just as
> necessary? Or is this why we're being suggested
> to write XML which can map well into RDF? ;)
One of the problems is that XML Schema names its types using QNAMES and
there isn't a straightforward general transform into URIrefs which are used
by RDF/OWL to name its classes. This remains a TAG issue and the XML Schema
WG is working on it, but since it is not yet solved, OWL can't use any such
future solution to test any implementations/interoperability today. Since we
can't test it the feature has been postponed for a later time.
> NB One sentence summary: I can assert myrdf:ZipCode owl:samePropertyAs
> but why can't I also assert myxml:ZipCode owl:sameDatatypeAs
How about this:
<owl:samePropertyAs rdf:resource="#ZipCode" />
Now you might imagine why doing this with XML datatypes would get tricky --
you'd need some XML datatype aware software that can compare "PSVI"s for
equality etc. Its alot easier to write simple datatype aware software that
understands equality for numbers, dates etc.