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Re: plain rules, please [was: Semantic Web Rule Language (SWRL) 0.5 released]

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 26 Nov 2003 10:59:57 -0500
Message-Id: <200311261559.hAQFxwY1017431@roke.hawke.org>
To: Bijan Parsia <bparsia@isr.umd.edu>
Cc: Dan Connolly <connolly@w3.org>, www-rdf-rules@w3.org

> On Wednesday, November 26, 2003, at 01:41 AM, Sandro Hawke wrote:
> [snip]
> > I can't speak for everyone on the committee, but I went along with
> > this because (1) it's important that the rule language be usable in
> > concert with OWL, and (2) several members of the JC were skeptical
> > that a rule language can be specified orthogonal to OWL and then
> > combined with it, while maintaining the proper semantics and desired
> > reasoner performance characteristics.
> 
> There is a sense, I think, in which OWL rules is orthogonal to OW (I 
> take it's combinability to be clear). There's no difficulty in using 
> OWL Rules with "plain" RDF,

Good point.    Some of the expressiveness (eg existentials in the
consequent) require OWL constructs, though, as I understand it.

 i.e., atoms restricted to using primitive 
> classes with no defined TBox or role hierarchy. It'd still be darned 
> expressive (e.g., you wouldn't really be able to eliminate various TBox 
> axioms and role hierarchy axioms since they are trivially expressible 
> as OWL Rules).
> 
> The is probably not the orthogonality people wanted :)

Yeah -- even if the vocabulary can be used by itself, the
specification is not orthogonal.

> >  I think the sense was that such
> > orthogonality "might be nice" or even "would be nice", but until the
> > details can be worked out, this 0.5 version seemed like a good
> > waypoint.  A future language with orthogonality should be able to be
> > compatible with this one, so letting folks begin coding to 0.5 seems
> > reasonable.
> 
> Compatible in what sense? I mean, "well, the orthogonal language needed 
> to be entirely disjoint with OWL, and heck, it's also disjoint with OWL 
> rules!" or "Once we figure out how to be usefully orthogonal and yet 
> combinable with OWL, we'll find that we've subsumed OWL rules or at 
> least fit in nicely with them"?

In the latter sense. 

> Personally, I don't yet have even a vague sense of this :(

I have a strong sense of it, but as I'm sometimes reminded, that
doesn't mean I'm right.  I think of RDF-based logics (RDFS, OWL, SWRL,
...) in terms of FOL axioms on sentences like "rdf(s,p,o)".  I think
this approach is suggested by LBase, and it's what Surnia (my quick
hack OWL implementation) does.  From this angle, orthogonality and
combinations of logics are fairly straightforward.

The downsides to this approach, I think, are (1) it doesn't really
tell you how to make practical implementations, just experimental ones
(eg throw it at a theorem prover); (2) the axioms are software, and so
unlikely to be perfectly correct.   (I'm not sure I buy #2, but I hear
it a lot.)

    -- sandro
Received on Wednesday, 26 November 2003 10:59:49 UTC

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