- From: Michael Kifer <kifer@cs.sunysb.edu>
- Date: Thu, 18 May 2006 22:18:01 -0400
- To: "Peter F. Patel-Schneider" <pfps@inf.unibz.it>
- Cc: public-rif-wg@w3.org
> From: Michael Kifer <kifer@cs.sunysb.edu> > Subject: Re: mappings between SWRL and Boley proposal > Date: Thu, 18 May 2006 21:22:07 -0400 > > > > > "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.) > > How is it more general? You are requiring the same interpretations on > either side of your condition, Not quite. If mappings between interpretations can be established then they don't have to be the same. > so it looks to me that two rule systems that > differe at all in their model theory will require a different RIF dialect. but basically - yes. If somebody comes up with a rule system that uses an unheard-of model theory then this would require a new dialect. I see no way around this short of telling people to stop innovating. > > > 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. > > OK, rule conditions. > > > 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. > > Sure. But I don't see that the proposal does much abstraction, if any, as > it drags each rule system's semantics into the RIF. Abstraction was a wrong word. Factoring out common parts is a better term. > > > > 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. > > It would be interesting to find out whether it can be done at all. > > > 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. > > OK, there may be a way of organizing the dialects, but that doesn't reduce > their number. This wasn't a goal. > > > 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. > > But even if you use the hybrid approach, isn't that a change to the > semantics and thus still generate a new dialect? Not really. If you treat OWL and RDF predicates as base relations whose extension is determined by their own semantics then no new semantics is needed. I am not sure about the existentials. They might have to be approximated by Skolem constants in some dialects. > > > > 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). > > I worry that the current state of the proposal is only adequate to > determine whether there is a syntactic mapping. I believe that both Gerd and I have explained this point quite adequately. --michael
Received on Friday, 19 May 2006 02:21:27 UTC