RE: How to add the constraining facets of XML schema.

> -----Original Message-----
> From: www-rdf-logic-request@w3.org [mailto:www-rdf-logic-request@w3.org]
> On Behalf Of Bijan Parsia
> Sent: Saturday, June 18, 2005 3:48 PM
> To: Geoff Chappell; 'Kenichi Taniuchi'; www-rdf-logic@w3.org
> Subject: RE: How to add the constraining facets of XML schema.
> 
> 
[...]
> >
> >Is it? I imagine most systems, if they support datatypes at all, are
> >supporting just the primitive types.
> 
> Well, our system (Pellet) does support derived, simple types, although
> there's no
> syntactic support, I suppose. Complex types would be nice, especially if
> we
> could do something more useful with XMLLiteral.

I wonder about the need for complex types. On the one hand, I suppose
they're nice from the perspective of being able to have islands of
closed-worldness within your rdf (at least I always assume an implicit
closed-worldness to xml, maybe that's not a universal belief?), but on the
other, I can imagine the debates about whether something should be
represented atomically in an complex xml literal or be represented by its
component parts in rdf. At a minimum, I guess complex values might be nice
for things like keeping units with values (and so avoid property names like
lengthInInches).

> > I'd agree that if you want to support
> >arbitrary derived types, the only suggested approach is to somehow
> reference
> >an external xsd (the pitfalls of which are one of the main topics of the
> >best practices doc I mentioned). But while I appreciate the goal of re-
> using
> >xml schema datatypes in rdf -- for purposes of not reinventing the wheel
> and
> >general interoperability -- I don't see why there can't exist an
> equivalent
> 
> It's making it *equivalent* that's hard. XML Schema is a beast, after all.
> 
> That being said, you could have a subset in RDF. That's what Jeff does.

I guess I've really only thinking about a subset. I'll have to look at what
he's done.
 
> Getting all that exactly right is a bit of a bear.
> 
> >means to describe a datatype wholly within rdf (it is a _description_
> >language after all and certainly hasn't been shy about describing aspects
> of
> >itself in other regards).
> 
> Not always the wisest thing :) A little shyness might make RDF more
> attractive :)
> 
[...]
> >
> >I'd hope that most reasoners would do the latter since it's just rdfs
> >reasoning.
> 
> Well, *on datatypes*. That's not RDFS reasoning, IIRC. There are pitfalls
> and
> rooms for interpretation.

Isn't it? 

By:
 	http://www.w3.org/TR/rdf-mt/#rulerdfs3 
and 
	http://www.w3.org/TR/rdf-mt/#rulerdfs10 

seems you should be able to know that any value of myproperty is a
xsd:integer (at least value-space-wise). Admittedly things might be a bit
murkier on the lexical-space side (and in practice, lack of support for
literals as subjects might thwart some reasoners from making the right
deduction). 

[...]
> >Yeah, I don't think it does violate anything.
> 
> Well, I still don't know your expected behavior, exactly. You do expect a
> clash if
> the integer is outside the constrained range, right?

Yes (plus hints to ui-generators). I've found facets are also handy on
strings - e.g. when you're auto-translating a sql schema into an ontology
and want to preserve the number of characters in a particular column/field.

 [...]
> > I chose
> >not to go this route because my tools currently can't look inside xml
> >literals during the reasoning process (except by treating them as
> strings).
> 
> Oy! that sucks. XMLLiterals are much neglected :(
> 
> Which tool is that, btw?

RDF Gateway [1]. To be clear, it supports xml literals fine wrt to
serialization etc. and the system can certainly consume xml in a variety of
ways. It just doesn't have built-ins to support inspecting xml literals as
xml during the reasoning process (other than by treating them as strings
with various string functions, regexp, etc.) -- so you can't easily create
rules based upon parts of the xml literal. Might be worth adding some sort
of xpath built-in to make these things available....

> Cheers,
> Bijan.

Best,

Geoff

[1] http://www.intellidimension.com/pages/site/products/rdfgateway.rsp

Received on Saturday, 18 June 2005 23:58:20 UTC