- From: pat hayes <phayes@ihmc.us>
- Date: Wed, 21 Jan 2004 13:04:29 -0600
- To: Bijan Parsia <bparsia@isr.umd.edu>
- Cc: public-sws-ig@w3.org
>On Jan 21, 2004, at 3:15 AM, Michael Kifer wrote: >[snip] >>>Indeed. There may be no differences, given my newer understanding of >>>how you intend that nonmon rules are to be used. I think we may have >>>been viewing the world from different metalevels, as it were. >> >>Suddenly the difference of opinion became fuzzy ... >> >>Unfortunately, nobody had the patience to read this far to find out that we >>actually agree :-) >[snip] > >I have, FWIW, but I'm not sure what to make of this agreement. Once >more, it may be at the level of nuts and bolts that the blood will >start to flow :) Actually, I don't think so. Getting a bit closer to the nuts and bolts makes things clearer (for me, at least). Its interesting that this disagreement/misunderstanding can be rooted in the differences between two world-views of what class-based reasoning is really *for*, one based on DL's evolution from logic, the other based on schemas considered as data descriptions. This difference of perspectives keeps coming up and seems to be very important: for example, does one think of range assertions as constraints (datatype) or simply as assertions (logic)? How about datatyping? And so on. We keep running into cases where people have divergent intuitions which can be traced back to the differences in attitude arising from these two world-views. Clearly at some level they are similar: Codd's Relational model and the DL logic-based semantics all agree on the ultimate nature of relations and classes; but the ways that the two communities think seem often to be sharply different. Im not sure how to characterize the difference, exactly, but it seems to be that the DB world-view sees a sharp distinction between different kinds of information, and tends to treat general facts as conditions imposed on concrete facts: meta-data as opposed to data. Distinctions like this may be operationally important but have no natural place in a logic-based perspective which historically has been largely motivated by the desire to unify divergent sources of information as far as possible into one uniform framework. If one thinks of a universally quantifier assertion as really being meta-data, i.e. as being about the ground facts rather than just another fact about the world, then this lends itself immediately to a host of what seem to someone coming from the logical tradition to be basically errors: things like considering Herbrand interpretations to be a fully adequate semantic theory; like finding various nonmonotonic techniques natural (even obvious) and thinking of quantifiers are essentially substitutional, all of which are anathema to logicians. And if you think that the more general assertion's chief purpose is to control, select or check the internal coherence of a body of ground data, then the purely logical account of quantification is inadequate or at any rate incomplete, since a combination like (forall (x) (R x x)) (not (R a a )) is of course inconsistent, but inconsistent in a special way: the second item is wrong, or should be rejected, as it fails to conform to the schema. The schema has more assertional force than the mere data in a DB world, since the schema is a kind of filter or guardian of the data. Logic has nothing to say about intuitions like this. Anyway, just rambling. It might be fun to try to get this divergence between world-views stated clearly, though, as the SW world seems to require DB folk and logic folk to be able to get along with one another. Pat >Cheers, >Bijan Parsia. -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Wednesday, 21 January 2004 14:12:02 UTC