Re: Nonmonotonic rules

>  >
>>  >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
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Received on Thursday, 22 January 2004 13:32:50 UTC