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Re: mappings between SWRL and Boley proposal

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Thu, 18 May 2006 21:22:07 -0400
To: "Peter F. Patel-Schneider" <pfps@inf.unibz.it>
Cc: public-rif-wg@w3.org
Message-ID: <16396.1148001727@kiferdesk>


"Peter F. Patel-Schneider" <pfps@inf.unibz.it> wrote:
>
> From: Michael Kifer <kifer@cs.sunysb.edu>
> Subject: Re: mappings between SWRL and Boley proposal 
> Date: Thu, 18 May 2006 15:00:32 -0400
> 
> > > From: Michael Kifer <kifer@cs.sunysb.edu>
> > > Subject: Re: mappings between SWRL and Boley proposal 
> > > Date: Thu, 18 May 2006 13:46:57 -0400
> > > 
> > > > > > > The proposal may not be sufficiently explicit about this,
> > > > > > > but it states that modeltheoretic satisfaction gives
> > > > > > > the meaning to conditions.
> > > > > > 
> > > > > > Yes, but where is this tied to the mappings?
> > > > > 
> > > > > This has not been made explicit in the proposal. So, 
> > > > > let's do it. [Harold and Michael, we are waiting for 
> > > > > your contribution to this.]
> > > > 
> > > > It was sufficiently explicit in the proposal and Peter knew exactly what
> > > > was meant.  The mapping is obviously supposed to satisfy the condition that
> > > >
> > > > I |= C  <->  I |= M(C)
> > > > 
> > > > for every interpretation appropriate for the dialect in question.  In a
> > > > more general case, M can also be a transformation on models, but this is
> > > > not required for Peter's case.
> > > 
> > > Well, where is the definition of interpretations and supports on the
> > > proposal side?  I don't see one.  Without such how can you talk about
> > > satisfying your condition above?
> > 
> > The proposal said:
> > 
> >     So, by semantics we mean the notion of satisfaction of a formula in the
> >     interpretations of the various RIF dialects.  For example, in FO, all
> >     first-order interpretations are appropriate. In LP, infinite Herbrand
> >     models are typically used. In LP with the well-founded semantics,
> >     3-valued Herbrand models are used. Stable model semantics uses only
> >     2-valued interpretations.
> 
> OK, so if in addition the proposal is extended by adding in the standard
> way of providing meaning to non-atomic syntactic constructs, then it can
> finally talk about satisfying the condition bove, provided that the rule
> formalism *exactly* matches up with one of the RIF "dialects" (to the
> extent of having the exact same set of interpretations).

It is actually more general than that. There are only a few different types
of interpretations (2-valued, 3-valued, etc.) so it would work for any kind
of dialect that uses one of these in its definition of semantics.
(Recall that the proposal talks only about the notion of satisfaction in an
interpretation.)

> However, what has the proposal provided beyond an alternative syntax for
> rules, then?

It was not an attempt to provide something new. And, if you noticed, there
was no syntax for rules -- only for their conditional part.

We are facing a pretty daunting task of providing an interchange format for
a bunch of very dissimilar formalisms whose only common theme is that they
are somehow "rule-based."  One way to approach this (we thought) was to try
to abstract some common parts of the syntax and semantics and then compose
dialects using building blocks. So, we abstracted the conditional part.
Other people (Paula&Francois) suggested that the event part can also be
abstracted.  The more we abstract -- the more uniform the resulting spec
will be.


> > There are different notions of interpretations and each comes with its own
> > definition of |=. When we say "first-order semantic structure", we mean a
> > particular definition of |=. A "3-valued well-founded model" has its own
> > definition, etc.
> 
> How many RIF dialects (i.e., semantics) are there going to be?
> 
> The proposal identifies four:
> 
> - FO (first order)
> - LP (logic programming)
> - PR (production rules)
> - RR (reactive rules)
> 
> But this can't be right, as the proposal has two different semantics for
> LP, and doesn't have a semantics for PR or RR.

More than that. The semantics of PR & RR wasn't touched because there are
people here who can do this better. But the idea was to construct dialects
out of building blocks. I hope that this could be gleaned from the
taxonomy, which I sent on Monday. Although it is cluttered, the point is
that many of the features there are orthogonal to each other and can be
combined in various ways. This is why there were so many nodes in that
taxonomy and many other nodes didn't even fit.

> As well, the proposal is
> going to need a semantics for rule systems using RDF, as the model theory
> of RDF is not exactly standard.  I forsee this approach leading to a
> different dialect for each rule system.

Not if we use the hybrid approach.


> > This was the intention, if the above wasn't sufficiently clear. Given that
> > this is a first draft (which didn't even pretend to be completely formal),
> > I claim that we can get some slack here.  Will try to clean it up in the
> > next iteration.
> 
> Sure you have lots of slack.  But, then why are we producing mappings into
> the proposal?  Let's clean it up first.  If it doesn't clean up well enough
> then we won't have wasted the effort of producing the mappings.  

I didn't propose to do the mappings. But I believe this was an informal
exercise to see if this meets the requirements that the different people
have (and to find where it falls short).


> On the other hand, if the mappings are only an alignment of rule systems
> syntax to the syntax of the proposal, then let's be clear about what we are
> doing (and what we aren't).  As well, let's make a separate document with
> just the syntax, so that it is clear to everyone that the rest of the
> proposal is not involved.
> 
> > > > By the way, the proposal didn't talk about these mappings, but it should
> > > > have been obvious that such mappings are needed and that the above
> > > > condition should be satisfied. Someone who proposed to define these
> > > > mappings in the telecon must have also had something like this in mind.
> > > 
> > > I had in mind, in part, trying to explicate what I felt was missing from
> > > the proposal and what was wrong with it.
> > 
> > This was too subtle for some of us to understand...
> 
> I'll be blunter next time.

Good.


	--michael  
Received on Friday, 19 May 2006 01:22:21 GMT

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