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Re: SEM: semantics for current proposal (why R disjoint V?)

From: Dan Connolly <connolly@w3.org>
Date: 05 Apr 2002 08:08:54 -0600
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: Libby Miller <Libby.Miller@bristol.ac.uk>, "Peter F. "Patel-Schneider <pfps@research.bell-labs.com>, webont <www-webont-wg@w3.org>
Message-Id: <1018015734.22258.38.camel@dirk>
On Fri, 2002-04-05 at 07:08, Ian Horrocks wrote:
> On March 21, Dan Connolly writes:
> > On Thu, 2002-03-21 at 14:28, Ian Horrocks wrote:
> > > On March 21, Libby Miller writes:
> > > > >
> > > > > As noted in the design discussions for DAML+OIL, I don't
> > > > > see sufficient justification for making V disjoint
> > > > > from R.
> > > > >
> > > > > It seems silly not to be able to talk about the intersection
> > > > > of two sets of strings, or UniqueProperty's whose
> > > > > range is dates, or whatever.
> > > 
> > > This means that any OWL reasoner has to take on responsibility for
> > > reasoning about types
> > 
> > I gather when you say "OWL reasoner" you mean a complete
> > reasoner.
> > 
> > I'm not very interested in such a thing.
> > 
> > Regular old horn-clause/datalog reasoners
> > (with some built-in predicates like
> > string:lessThan and such) seem
> > to get me what I need pretty well.
> 
> Dan,
> 
> It seems that, on the basis of a few toy examples where using ad-hoc
> reasoning seems give the results you want/expect, you conclude that
> this will be appropriate/adequate for all applications.

No, just for an interesting class of applications.

By the way, if you consider
formalizing the operations of W3C[1]
to be a toy example, I'm interested to know what
sort of applications you would take seriously.

>  I don't find
> this argument very convincing. 

As I say, I didn't make that argument.

I'm arguing that we can advance the state of the art
without a completeness requirement.

> Even w.r.t. ontology level reasoning I expect things to rapidly get
> large and complex enough that humans wont be able to check all
> inferences - we will just have to trust that the reasoner got it
> right. Soundness is therefore essential, and completeness highly
> desirable.

Yes, soundness is essential.

I don't see why completeness is all that interesting
in the general case. I expect various reasoners
to be complete for various classes of problems.

> For example, when multiple processes are interacting, some
> action may be taken by one process on the basis of a non-inference by
> another process,

That's non-monotonic reasoning. Part of life in the semantic
web is: don't do that (without explicit license).

> so incompleteness can easily lead to "unsoundness".

Unsoundness can result from all sorts of bugs; this
is just one of them.

Actually, unsound/heuristic reasoning can be pretty interesting,
as long as it's not confused with formal reasoning; e.g.

	I conclude based on your recent buying patterns
	that the following products are likely to be
	interesting to you: X, Y, Z.

	I didn't arrive at this conclusion based on
	sound reasoning, so take the recommendations
	with a grain of salt.

or

	I conclude, based on a search of my extensive
	holdings, that there are no court cases
	in that jurisdiction involving chimpanzees and volkswagens.

	Digitally signed,
	The BigLaw online service.



> As far as the disjointness of object/data domains and properties is
> concerned, there are also good pragmatic reasons for this, including
> the ability to use hybrid designs for OWL reasoners, i.e., the ability
> for an owl "object class" reasoner implementation to "bolt on" a type
> checker for arbitrary type systems.

That seems like an interesting software architecture for
a certain class of problems. But why should it constrain
the language we're designing?

If such a system came across some data where "3" was
a member of a class, I'd expect it to throw an exception ala:

	Sorry, this software is limited to problems
	where the datatypes and the class members are disjoint.
	I can't compute the answer you asked for.

not

	Sorry, your data doesn't conform to the language specification.


[1] e.g. we're formalizing our tech report digital library,
and the workflow around it.
  http://www.w3.org/2002/01/tr-automation/

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Friday, 5 April 2002 09:08:41 GMT

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