- From: pat hayes <phayes@ihmc.us>
- Date: Thu, 22 Jan 2004 12:30:18 -0600
- To: Michael Kifer <kifer@cs.stonybrook.edu>
- Cc: Bijan Parsia <bparsia@isr.umd.edu>, public-sws-ig@w3.org
> > >> >On Jan 21, 2004, at 3:15 AM, Michael Kifer wrote: > > >[snip] ><snip> > > 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. > >Yes, I think this is very accurate. >With respect to the Semantic Web, this problem can be very serious. >People who have training in different fields might use (or misuse) the same >formalisms differently. Yep. There are traces of this in the email archives of the various WGs already, and in some of the public comment/discussions. > > .... 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. > >*Classical* logic has nothing to say about it. This doesn't mean that you >can't define a logic in which meta-info is treated differently from >"regular" data. Oh, sure. You can define a logic to do just about anything. But I don't trust these proposals until I see some kind of semantic justification for the distinctions they draw. (Neednt be *classical* semantic, but somehow non-arbitrary.) I confess to not (yet) being familiar enough with F-logic to know if it has such a justification. >F-logic does this. It defines what it means to conform to >the meta-data (although not completely satisfactorily from the point of >view of programming languages). >There is also Typed Predicate Calculus (LICS-91), which espouses the same >idea (which later went into F-logic). > >The basic idea is that there is a notion of well-typed >interpretations and only >those things are acceptable as models. So, you are not supposed to derive >things that violate the meta-data. And of course 'classical' sorted and typed logics make a similar distinction, but they encode it as a purely syntactic matter. I doubt if this is adequate for our purposes here, however. Can you point me to any kind of general discussion of these issues from a DB perspective? Pat -- --------------------------------------------------------------------- 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 Thursday, 22 January 2004 13:32:50 UTC