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Re: XML Schema datatypes

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Thu, 15 Nov 2007 02:33:35 +0000
Message-Id: <92214F9D-4150-4B87-98D4-E92FBF579FE3@cs.man.ac.uk>
Cc: "Web Ontology Language (OWL) Working Group WG" <public-owl-wg@w3.org>
To: Carsten Lutz <clu@tcs.inf.tu-dresden.de>

On Nov 14, 2007, at 7:09 PM, Carsten Lutz wrote:
[snip]
> But this is not what a user excepts since (s)he is working with an
> ontology, i.e., doing a *conceptual modelling*, so she should abstract
> away from details such as representation of numbers and think of  
> floats
> as rationals or reals. These are dense, so the user expects the above
> intersection to be non-emoty.
[snip]

> ----------------------------------------------------------------------
>
> 3. XML Schema is not a good choice for defining datatypes.
>
> XML Schema is a schema language for XML, i.e., it describes
> semi-structured data stored in the form of an XML document.
> It's very good for that purpose, because if you store data,
> it is important to consider the details of storage, which
> usually involves boundedness, fixed precision, and rounding.
>
> *We* are *not* defining a schema language for (stored) data in the
> sense of XML Schema. So it is a valid question whether or not the XML
> Schema datatypes are also good for our (different) purposes. I believe
> they are not.

I think this is too strong. Sometimes users use OWL for *high level*  
conceptual modeling, but sometimes one is refining the conceptual  
model a bit based on some more concrete aspects. why should they have  
to switch out from OWL just because they need to account for  
representation limits? What about modeling database schemas?

And conceptual modeling isn't the only thing people do with OWL.  
People do information integration which can require details about the  
types (consider either ETL or distributed query). Or when reducing  
other formalisms, like policy languages such as WS-Policy or XACML,  
to OWL, it can matter that you have the actual datatypes involved.

Finally, people *do* user RDF and OWL directly to work with semi- 
structured data.

So, I see your argument as supporting adding some additional, more  
general types, to better support CM, not as an argument for  
eliminating various representationally specific numeric types.

As with numeric methods genearlly, the user must exercise care.

> We are defining an ontology language with a declarative semantics.

I don't see that declarativity is an issue here.

> As
> the above examples show (and there are tons more), we get all sorts of
> oddities from the combination of (i) an expressive logic that has a
> declarative semantics

Again, declarativeness doesn't seem to be relevant.

> and (ii) the bounded datatypes of XML schema.

Boundedness is an issue, but you can get that with integers and min  
and max. Which we have.

> As
> the literature on concrete domains in description logics shows, there
> are no such problems if you work with unbounded datatypes such as the
> integers or the rationals (the reals are problematic for reasons that
> are not related to boundedness or unboundedness; not to be discussed
> here). I agree with Jeremy that these problems, which are already
> present in OWL 1.0, get more relevant when switching from unary to
> n-ary datatypes. Still, it seems strange to argue against n-ary
> datatypes based on a problem that is present already with unary
> datatypes

I strongly agree with this. The problems exist in either case, and I  
would go further and say that the are not so much stronger in the n- 
ary case to warrant throwing out n-ary.

> and that, when defining OWL 1.1, we have the chance to fix.

I don't see that as a fix. And if the issue is merely boundedness  
then we'd have to chuck user defined datatypes on the integers.

Cheers,
Bijan.
Received on Thursday, 15 November 2007 02:34:13 GMT

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