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Re: Converting SHOE to RDF: about 2/3 done; some gotchas

From: Stefan Decker <stefan@db.stanford.edu>
Date: Sat, 13 May 2000 09:24:45 -0700
Message-Id: <4.2.0.58.20000513012150.0292c840@db.stanford.edu>
To: Sean Luke <seanl@cs.umd.edu>
Cc: www-rdf-interest@w3.org
Hi Sean,

> > > Also, as I understand it way namespaces are used in RDF is
> > > only to uniquely identify what object you're talking about, not which
> > > sets of definitions you subscribe to. Thus, if I state that I am
> > > Web_Developer, then do I also imply that I am a Silly_Person?
> >
> > If you say P and P->Q, then you imply Q, yes. But
> > if you say P and somebody else says P->Q, then a third
> > party may or may not decide to trust you both enough
> > to conclude Q.
>
>What if a third party Foo says P->Q, you rely on this to make all sorts of
>statements about P under the assumption that your clients will use Foo's
>claim to understand that you're really talking about Q, and then Foo drops
>off the face of the earth?  Say, because the ILOVEYOU virus brings down
>their system for a week. They're still very trustworthy: everything they
>say is true.  But right now they're not saying anything, and your clients
>don't find their stuff and so interpret your semantics in a different way
>than you did when you posted your data originally.  Or Foo updated its
>claims and dropped a few statements that you relied on, not knowing that
>you were doing so.  You're left hanging in the wind.
But i want to define links between knowledge pieces and point to
different servers on the web.
I have to deal with glitches then, but i also have to deal
with the same glitches now (eg. when i encounter a broken link in
a HTML page).

>It seems to me that trust isn't a great model for this kind of stuff in a
>distributed, uncontrolled environment. I think that dealing with the
>weirdness caused by a lack of control inherent in a distributed system is
>one of the features that RDF needs to work more on.  Because RDF lets
>"anyone say anything about anything", with no notion of authority at all,
>then people are free to redefine the semantics of a language in a very
>fine-grained, highly distributed fashion.  Combine this with a cooperative
>reliance on who said what about what in order to understand the proper
>semantics of some claim X, and you're gonna see a lot of semantic
>misinterpretation as little parts of the distributed RDF web come up and
>down.
>
>SHOE's model counters this in two ways, which Jeff is getting at I think.
>First, it separates schema from data, which at least attempts to provide
>*some* semblence of authority, or at least a well-defined semantic
>language so we're very clear on what I intend to be inferred when I say
>thing Foo.

But is actually also possible for RDF. An RDF-Schema (or Sergeys UML-RDFSchema)
can define any language for RDF. One is free to adopt a formal semantics for
the language if this is useful - this is actually the way currently
OIL goes (see http://www.ontoknowlege.org/OIL ).
So you have the same separation of schema and data - with the freedom
to define any Knowledge Representation Language on top of RDF - and i
don't just count logic based formalisms as Knowledge Representation Languages.
What about Petri Nets or finite state machines (see again Sergeys UML model)
(which are used to represent dynamic knowledge in a declarative way)?
How would a Petri Net (and instances of Petri Nets) be defined in SHOE?

>RDF would work great in a "sandbox environment" typical of most KR
>systems, where the system has the entire body of knowledge (so to speak)

(RDF is not a Knowledge Representation system at all.
RDF just provides a lightweight object model to define other
languages on top of RDF - not necessarily typical KR languages.)

 >stored internally and so can interpret statements in its system under the
 >semantics of the full universe of facts at its disposal.  But I think that
 >RDF does not take into consideration the uncomfortable fact that the web
 >is not a sandbox.  People say anything they want, even trusted ones.  And
 >they can stop saying these things at any time, and for any reason.
 >Relying on the availability, correctness, and completeness of others'
 >statements in order to put your own into context is pretty dangerous.
Isn't it equally  as dangerous to a link to another HTML-page from
your own page, since you can't guarantee that the other HTML-page will
be available an hour late?

I agree: one can't rely on concepts like
correctness and completeness in the conventional use anymore (as eg. known
from Reasoning in First-Order Logic).
So we need to find other concepts.


Best,
         Stefan
Received on Saturday, 13 May 2000 12:17:57 GMT

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