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DTTF: high-level summary (attempt)

From: Massimo Marchiori <massimo@w3.org>
Date: Thu, 2 May 2002 12:11:51 -0400
Message-Id: <200205021611.MAA23226@tux.w3.org>
To: www-webont-wg@w3.org

[pant pant...
catching up on the DTTF after a hectic week culminated in 5 new Query drafts]

Ok, I don't know to what thread to reply, and how to avoid sending 4 different ones...
Well, let's just try to draw a line, and see where we are.

Is is true there's some weak consensus that, bad or good, we can try to leave RDFCore
out, and work out the solution in WOWG? Or, is there still somebody saying he
can't live with this? This is useful to do a first little step: let the semweb cg
know that this dependency on RDFCore is discharged.

Secondarily, the base two points. I think there are two main issues boiling up
in all the threads.
a) One is Peter's point, about paradoxes and expressive power.
b) One is Pat & Peter point, about semantic extensions.

They are somehow related (b somehow subsumes a), yet can be usefully distinguished.
a) essentially says, look, what we have is very powerful (essentially, graph
construction), and we risk that the resulting language is not well defined
(which implies, yes, a disaster).
b) essentially says, there are big troubles in general, to do a semantic 
extension of RDF.

Now, I think all the DTTFers are right (errr, is this a paradox? ;) when they
claim respectively that a) and b) can't be solved with RDF as is (RDF: bad),
and that a) and b) can in fact be solved.
They are all right, because each starts from different assumptions, making
their reasoning perfectly valid, and resulting in us clashing on the conclusions,
rather then on the premises.

Now, on a) and b), the personal viewpoint on "how it can be done" without 
changing RDF (so, the context).
On a):
+ Yes, this is a big problem. but a way out is to define the semantics of OWL
using graph rewriting (cf. http://lists.w3.org/Archives/Public/www-rdf-comments/2002AprJun/0018.html
for a subset of a possible definition for RDF semantics). This can be seen as 
"considering the right syntax" (so, similar to Peter's syntactical constraints, only
that the constraints are not on the graph, but on the rules used to extract 
the semantics).
This works because it doesn't follow the "everything denotes", which is the understood
assumption that, I think, is based on the RDF-cant-work-here argument (which is correct,
under this assumption!).

Onto on b):
And, yes, this is related to the semantical extension problem. I think the understood
assumption of the RDF-cant-work-argument has been that you have to model the semantics
of an extension *using the same domain* (so, essentially like a semantical embedding).
And under this assumption, yes, this is correct, RDF can't probably be used here
(unless changing it with dark triples or similar).
The way out here is to drop the assumption to use a semantical embedding: the domains
of interpretations can be different. Doing so, we earn in flexibility of extension,
and we lose something in semantic interoperability.

I can provide extensive details on both a) and b) on demand, but before doing so (i.e., 
debate on the correctness of a specific assumptions => conclusions approach), it's way more 
important to notice the assumptions we come from. Under some assumption (that were natural 
and almost understood for me, but are likely not at all for others) there is a way out. 
Under others assumptions (reasonable as well, just different), there's likely no way out other than 
doing some heavy changes to RDF (personal view, but I do agree with Peter and Pat, once
realized the context/assumptions they are reasoning in).

Is this a fair high-level summary?
-M
Received on Thursday, 2 May 2002 12:11:50 GMT

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