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Re: Final version of semantics

From: Jos De_Roo <jos.deroo@agfa.com>
Date: Thu, 13 Nov 2003 00:53:24 +0100
To: "pat hayes <phayes" <phayes@ihmc.us>
Cc: "w3c-rdfcore-wg" <w3c-rdfcore-wg@w3.org>
Message-ID: <OFA0F81C8E.04C7248C-ONC1256DDC.008074C4-C1256DDC.00833B7A@agfa.be>

Pat - this is a milestone! (was surprised to see such a Subject:)
It's also the first time as far as I can remember that you don't
mention a URI for that version, so it must be special :-)
but I'm sure it will show up soon at it's deserved place.

The only point I have is that wrt 6. we have not implemented
things as Triple(x,y,z) but as y(x,z) which was a choice.

Still can't believe it...

Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/

                      pat hayes                                                                                                         
                      <phayes@ihmc.us>          To:       w3c-rdfcore-wg@w3.org                                                         
                      Sent by:                  cc:       Graham Klyne <gk@ninebynine.org>                                              
                      w3c-rdfcore-wg-req        Subject:  Final version of semantics                                                    
                      2003-11-13 12:13                                                                                                  

Guys, in the interests of full disclosure, here's a summary of the changes
made to the semantics document in the last few days. I actually think that
this is now *all*.

1. Section subheadings added/changed as per

2. "name" now includes plain literals, so vocabularies (= sets of names)
also may contain plain literals. They are not obliged to, so all old
vocabularies are still new vocabularies.

3. 'proper instance' now allows substitution of a plain literal for a

4.  semantic conditions on simple interpretations of a vocabulary V are now
restricted to the plain literals in V (as they were formerly for the URIs
and typed literals. )

The effect of 2-4 is that all referring expressions (URIrefs and literals)
are treated uniformly, and interpretations of a graph are only obliged to
interpret the symbols which occur in the graph. All of this is conventional
and makes the RDF MT more 'normal'. For justification of why it was needed,
see Herman's recent comment on the failure of the RDFS entailment lemma
(see "To give an example, let A be a URI reference" et seq)
No changes to any test cases or entailments arise.

5.  minor editorial changes arising from 2-4 above, eg "name or plain
literal" -> "name" in several places, and the example in figure 1 now has
the literals listed in its vocabulary explicitly.

6. Text added in 1.1 Technical note (Informative):
"Readers who are familiar with conventional logical semantics may find it
useful to think of RDF as a version of existential binary relational logic
in which relations are first-class entities in the universe of
quantification. Such a logic can be obtained by encoding the relational
atom R(a,b) into a conventional logical syntax, using a notional
three-place relation Triple(a,R,b); the basic semantic described here can
be reconstructed from this intuition by defining the extension of y as the
set {<x,z> : Triple(x,y,z)} and noting that this would be precisely the
denotation of R in the conventional Tarskian model theory of the original
form R(a,b) of the relational atom. This construction can also be traced in
the semantics of the Lbase axiomatic description [LBASE]."

This point was raised by at least 3 people at ISWC and in other working
groups, so I thought it might be worth drawing attention to.

7. Other minor editorial suggested by Herman, eg "and A(E) is defined"
added in the third semantic condition table. None of these change meanings,
only clarify or correct errors.

8. The definitions of the Hebrand interpretations in the proof appendix
have been simplified somewhat, since they are no longer required to
interpret all plain literals.  The definition of the 'sur' construction in
the RDFS entailment lemma proof has been clarified; several explanatory
paragraphs have been added to make the proofs easier to follow, and some
typos corrected (which also helps, of course.) Again, for discussion and
motivation see Herman's recent email comments.

9. As well as the above, the change log notes the
_:x rdf:type rdfs:ContainerMembershipProperty .
empty entailment case discussed in earlier emails.



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Received on Wednesday, 12 November 2003 18:53:31 UTC

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