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continuing technical issues in the RDF Semantics document

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 22 Aug 2003 10:56:44 -0400 (EDT)
Message-Id: <20030822.105644.33666792.pfps@research.bell-labs.com>
To: www-rdf-comments@w3.org

The current version of the RDF Semantics document, titled RDF Semantics
Editors Draft August 21, has continuing technical issues that I discovered
in a quick, incomplete pass this morning.


The document does not define ``character string'' or ``language tag''.
These need precise definitions as the definition of simple interpretations
depends on them.

In the examples (in Section 1.4), the pictures do not correspond to the
text, as they have Thing 1 in the domain whereas the text has 1 in the
domain.  The first picture also has the incorrect claim that ``The universe
has just two things in it.''

The set of rdf-interpretations has changed significantly.  An
rdf-interpretation need not have domain elements corresponding to every
possible XML literal.  This does not affect RDF, but may be a problem for
languages built on top of RDF.

There are conditions imposed on the non-core RDF vocabulary by
rdf-interpretations, counter to several claims in the document.

The redundancy of ``all but one of the RDF axiomatic triples'' cannot be
derived from ``the RDFS axiomatic triples and the smenatic conditions on
rdfs:domain and rdfs:range''.  It also requires the semantic condition for
ICEXT to make these derivations.  As well, the semantic conditions for
rdfs:range are not needed.

The definition of the Herbrand interpretation of a graph has all
well-formed XML literals in LV, which is permissable, but incorrectly
states that these are required to be in LV, and makes Herbrand
interpretations non-minimal.  It is not the case that a
Herbrand interpretations is a simple interpretation - consider the Herbrand
interpretation of the empty graph.  As well, Herbrand interpretations abide
by part of the RDF meaning of rdf:type, which also makes them non-minimal.  

The Herbrand lemma is false as Herbrand interpretations are non-minimal.

The problems with Herbrand interpretations make the proof othe RDF
entailment lemma and the RDFS entailment lemma suspect.

The proof of the RDF entailment lemma is suspect in other ways, as the
rdf-interpretation constructed (H') appears to have both XML values and
blank nodes in the class extension of rdf:XMLLiteral.  The details of XML
literals are sufficiently arcane that I cannot determine whether this is
permissable.


On a minor note, the definition of proper instance means that
	<ex:a> <ex:b> "a" .
is not a proper instance of 
	<ex:a> <ex:b> _:xx .
This affects the definition of lean graphs, and reduces the scope of the
anonymity lemma.



Peter F. Patel-Schneider
Received on Saturday, 23 August 2003 02:52:50 GMT

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