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Final version of semantics

From: pat hayes <phayes@ihmc.us>
Date: Wed, 12 Nov 2003 17:13:25 -0600
Message-Id: <p06001f1abbd8662cf8c3@[10.1.31.1]>
To: w3c-rdfcore-wg@w3.org
Cc: Graham Klyne <gk@ninebynine.org>
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 
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2003Nov/0051.html

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 bnode.

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 proof
http://lists.w3.org/Archives/Public/www-rdf-comments/2003OctDec/0150.html 
(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.

Pat

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Received on Wednesday, 12 November 2003 18:13:27 EST

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