W3C home > Mailing lists > Public > www-rdf-logic@w3.org > June 2001

Re: Why? Re: rdf as a base for other languages

From: Lynn Andrea Stein <lynn.stein@olin.edu>
Date: Fri, 01 Jun 2001 18:38:46 -0400
Message-ID: <3B181976.5B7C9559@olin.edu>
To: pat hayes <phayes@ai.uwf.edu>
CC: www-rdf-logic@w3.org
Disclaimer:  I wrote this considerably after I had intended to leave my office,
and it is not well edited or concise.  I considered sending it to Pat offline, but
decided to mail it to the list so that it would be available for anyone who cares
to slog through it.  It is possible that I will be more articulate or concise on
Monday.

pat hayes wrote:

> > > In order to decide the truth of any statement "X" I cannot simply test
> > > whether it is or is not a direct member of the set of Statements. If it is
> > > not a member, "X" might still be true, because it is inferred
> >from the other
> > > statements as you describe.
> >
> >This is essentially always true, unless you forbid inference and close the set
> >of sentences you're considering.  What's important is what we (minimally)
> >require that you be able to tell/infer and what we (maximally) permit you to
> >infer and what we do about any discrepancy that (almost inevitably) remains
> >between the two.
>
> I don't see there being anything here to do with permissions or
> requirements. How can one website emit such constraints on another
> web agent's actions? There arent any guards here.

This is social contract talk.  Let me try to put it into a more purely logical
language.  (I do think, as I've said elsewhere, that part of the misunderstanding
going on here is between a logical understanding of these languages and an
effective computation understanding of the same languages.  These are pretty
radically different (and often entirely incompatible) views.

In a more logical framework, if I say:

(forall P. P(x) -> Q(x))

what I mean -- what inferences are licensed, e.g., -- depends on the logic I'm
using to interpret this statement.

Since RDF doesn't come with its inference rules predefined, it's not obvious which
inferences are licensed (i.e., what logic RDF+rules is).

Now we *have* to switch into the effective computation world:  It is likely that
different users of RDF will in fact choose to calculate different sets of
consequences.  It is also likely that some minimal (perhaps empty) set of
consequences will be deemed to be "required" in order to be compliant with the
RDF+rules language and some larger set will be "consistent".  That is, RDF+rules
will be a family of logics with at least one middle category.  Think of it as a
modal system with a gap between necessary and possible.

> > > So why say that statements are true just because they are members of this
> > > set? ...
> >
> > > To me, stating that each statement in Statements is a fact does not gain me
> > > anything (in ease of inferencing) and costs me alot (of cumbersomeness and
> > > confusion).
> >
> >Well, not "are true" and not "is a fact", but "is asserted by the
> >document", at
> >least, which may be the same as far as your concern goes.
>
> No, no. That is what "assert" MEANS.

No, it's *not*.  Not in a speaker-relative context.  Not in a logic of beliefs.
Not in almost any modal context.  Assert here is a modality.  Sheesh, Pat, you
know better than this.

> Look, if I assert (note: *assert*) the following sentence: "The sun
> is shining.", then while of course you are free to believe or
> disbelieve me, or indeed to draw all sorts of conclusions about me,
> it remains the case that what I said was that the sun was shining.
> That is not a sentence, but a claim about the way the world is: it is
> such as to make the sentence (that I asserted) true. You may observe
> me and correctly say "Pat asserted: "The sun was shining" " , much in
> the way that you might observe a frog and correctly say: "The frog
> said: "Graaak" ", but that observation does not constitute an
> exchange of content, and what you have asserted is not what I said.

Absolutely.  But in RDF, if you said it, YOU asserted it.  Assert_PAT (Shining
sun).  (Use the appropriately indexed modal.)  It's hard to imagine how a logic
based on RDF as currently used and spec'd could treat this as anything other than
a requirement for the following interpretation: In the possible worlds
corresponding to your perspectives,  (Shining sun) is true.

>
> If we are having a conversation under normal rules of mutual
> cooperative communication, then a basic act of communication has
> taken place not when you make an observation about my utterance, but
> when you interpret the *content* of that utterance and accept it, ie
> when my asserting "the sun is shining" leads you to believe that the
> sun is indeed shining. I presume that the basic idea of RDF (and DAML
> and OIL, etc.) is that they are primarily intended to be used to
> convey content in roughly this way, though of course greatly
> simplified since it occurs between mechanical rather than human
> agents. The wide world being what it is, no doubt issues of trust and
> cynicism may well arise, but these surely are intended to be
> concerned with the *content* of what the RDF (etc.) is encoding, not
> about its *form*. If the primary goal of all this effort is just to
> enable one agent to send some symbolic shapes to another to enable
> the recipient to assert something of the form "A sent me the
> following string:"kdjglafldgfla" " , then there seems to be little
> point in the entire enterprise.

Yes.  Agreed.

> > Certainly the
> >benefit (which is nonetheless present for some and in some applications) comes
> >at a cost (for those who buy into inference as a given).
> >
> >I am under the impression that assertion by the document of statements
> >contained within the document is a fundamental tenet of RDF and there's no
> >changing it without dropping RDF. Assertion is *not* the same as truth of all
> >statements or documents,
>
> It is the claim that they are true, however. The two are closely linked.

Again, BY an agent.  You can't just drop the agents out.  Logics of belief.  We've
been through this all already, at least a decade ago.

Lynn

> > but it is certainly something one could question if
> >one were considering RDF or not RDF.  And I might take your approach in this
> >respect if I were building a language from scratch.
>
> Pat
>
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Received on Friday, 1 June 2001 18:38:55 GMT

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