Re: Nonmonotonic rules

>
>>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.
>
>Yes. Stefan Decker and I hit this clash last march in Japan.

I have this wonderful image of you and Stefan as sumo wrestlers.

>>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)?
>
>Yep. It seems particularly critical in the service realm, as Stefan 
>again drove home forcefully in Florida last fall. If you describe an 
>input's type using an OWL class, at invocation time, what 
>information must you know, and know to send?

Hmm. How about having a Rule here, a kind of service-best-practices 
Declaration from On High, to the effect that ontologies for use in 
Service applications ought to be constructed so that just being in 
the class, or maybe classes, is enough. If the input's type is 
described by membership in a class C or classes C1... Cn, then the 
ontology defining C ought to be enough for you to either infer the 
information you want, or to be able to figure out what other queries 
you might need to make. Then you have at least a snowball's chance of 
figuring them out before-hand, and so advertising in your type 
description what it is that you need to know, by listing the relevant 
classes or inventing a special class.

>If the class is Person and person restricted onProperty childOf 
>someValuesFrom Person...do you have to send all the information 
>about the parents as well?

I'd say the answer ought to be, no, unless the class description is 
something like 'person with parents', members of which would be 
triples of people, rather than just people.

>What if the individual happens to be  a member of parent and 
>soccerCoach (where neither is a subclass of the other)? Do you send 
>all you know?

Exactly, it could never end. It has to be up to the one requesting 
the information to say what is needed, surely (?).

>What if you're knowledge is incomplete, i.e., you know its a parent 
>but don't know any further details about the children? For some 
>services that might matter, others not.
>This difference isn't usefully expressed by the simple declaration of type.

It could be, if there was a global convention to that effect. It 
would require people to define the classes they needed (such as 
classes of person-parent-parent triples): in other words, the global 
conventions would drive the ontologies, rather than the reverse. 
Which is as it should be, right? We should make our ontologies work 
for us, not the other way round.

>(Stefan, feel free to jump in if I'm mangling your point.)
>
>It seems to me to be a severe problem: You are likely to often have 
>too much *and* too little information.

Nothing that we can do about that, but the real problem here seems to 
be how to indicate what information to communicate, rather than what 
information is actually there. If information is genuinely missing 
then nothing can be done: and there will always be surplus 
information that isn't required for some task at hand.

>
>>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.
>
>Also, as is apropos, the handling of incomplete information, and 
>thus the kind of (and efficiency) of the sort of reasoning you can 
>do.

Right. I guess that's a good way to think about nonmon reasoning: its 
a way of (perhaps temporarily) filling in missing information with a 
best guess.

>>  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.
>
>I tend to think of this as a consequence of the expressivity of the 
>formalism. TBoxs and ABoxs can be pretty distinct, at least until 
>you reach a certain level of expressivity.
>
>>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.
>
>Oh come! Substiutional quantification rules! :)

I take it that this is intended as a joke. However, as Im sure you 
must be aware, logicians tend to view jokes about quantification in 
the same way that airline baggage inspectors view jokes about bombs. 
Sniff.

>
>>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.
>
>Yes.

OK, who is going to write it?

Pat
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Received on Thursday, 22 January 2004 13:32:46 UTC