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Re: the idea of a 'reserved' vocabulary

From: Jonathan Borden <jonathan@openhealth.org>
Date: Thu, 13 Jun 2002 21:33:20 -0400
Message-ID: <011101c21343$77ca5300$0201a8c0@ne.mediaone.net>
To: "patrick hayes" <phayes@ai.uwf.edu>
Cc: <w3c-rdfcore-wg@w3.org>

patrick hayes wrote:

> Here's a rough draft of what Id like to say in the RDF MT document
> about 'reserved' (we don't say 'dark' these says) vocabulary, to give
> you an idea of what is being proposed here.
> ------
> What does it mean to assert an RDF graph? The normal answer is that
> each triple can be read as a simple proposition, and the graph as a
> whole represents the conjunction of all of these propositions, so
> that what is asserted is the content of all the triples in the graph.
> Asserting a triple amounts to saying that it is true, and what that
> means, in turn, depends on what defines the meanings of the terms
> used in the graph. Before discussing that in more detail, we first
> note that it is also possible to use RDF triples simply as a
> data-structuring mechanism for encoding expressions of other
> languages which have a more complex syntax. If those 'encoding'
> triples are regarded as assertions in the same way as other triples,
> complexities can arise because the meaning they would have when seen
> simply as RDF assertions might not correspond to their intended
> interpretation in the other language. To accommodate such encodings
> and avoid these complications, we allow that some urirefs may be
> declared to be 'reserved'. Triples using urirefs from any reserved
> vocabulary can be present in an RDF graph but do not themselves make
> any RDF assertions. They may, however, be part of an encoding of
> expressions in some other language which itself may be asserted by
> the RDF graph in question, according to the semantic rules of that
> other language. We note that an RDF parser or processor is not
> required to treat such triples in any special way, unless it also
> needs to access the content expressed in that other language encoded
> in an RDF graph.
> Since reserving a vocabulary effects the meaning of RDF, the
> authority to declare a uriref or urirefs 'reserved' in this sense
> rests with the W3C.  A uriref or set of urirefs is reserved only if
> it is declared to be so by a W3C Recommendation. In particular,
> reserving a vocabulary cannot be done by simply asserting on a
> webpage that it is to be considered reserved. There is no way to
> state in RDF, or any language encoded in RDF, that a uriref is
> reserved, or for any RDF document to entail this as a consequence.
> -----
> And then the basic MT rule for I(E) is slightly modified so that it reads:
> If E is a triple S P O . then I(E)=true if S, P and O are not reserved and
> -----
> That is all that is being suggested. And yes, this is the old
> 'unasserted triples' idea in a slightly updated form.

This looks like it meets the goals of WebOnt/OWL in that:

1) No intrusive changes to the RDF syntax
2) It would enable WebOnt to use certain RDF triples as syntax for which the
OWL MT might itself give meaning as far as OWL itself is concerned.
3) My assumption is that WebOnt/OWL would be given license to decide which
triples it were to employ as 'reserved' -- as long as these decisions were
documented in the OWL specifications -- and that such decisions would not
interfere with RDF, nor would RDF need concern itself with such OWL details.

This looks like it meets the goals of RDFCore WG in that:

1) no changes to RDF syntax
2) minimal changes to RDF MT

Under the circumstances, particularly given the tight schedule RDFCore is
on, this is a good option and leaves room for future specifications (e.g.
RDF 2, DAML-S, DAML-R) to define their own MTs, as needed, in a coherent
fashion. Ultimately I would like the issue of context/color dealt with in a
proper fashion e.g.perhaps

These sorts of issues underscore the importance of something like Lbase in
providing a mechanism to coordinate various specifications and their
corresponding model theories which define the various semantic web
languages. I appreciate that issuing a WD corresponding to Lbase may be
outside the current RDFCore WG charter but perhaps the RDF MT could be
aligned, as you have suggested, with Lbase and Lbase itself taken up by
either WebOnt or some more general SemWeb activity as is viewed appropriate.
I could make an argument that this need for coordination, and hence Lbase
itself, has grown out of the issues raised during the OWL/RDF layering
discussions and hence within the WebOnt charter but in any case it is
important work and deserves a good home. Under the circumstances, seeing as
how all the RDFCore folks have already been working overtime, as long as
this gives WebOnt license to get on with OWL, we ought thank you and let you
wrap your own work ASAP.

Received on Thursday, 13 June 2002 21:46:54 UTC

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