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issues with the 5 Sept version of RDF Semantics

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sun, 31 Aug 2003 13:55:26 -0400 (EDT)
Message-Id: <20030831.135526.68557469.pfps@research.bell-labs.com>
To: www-rdf-comments@w3.org

Technical Issues with the RDF Semantics Document
(version dated 5 September 2003)


How can there be ``two versions of the same semantic theory'' that ``differ
slightly''?  Either they are the same or they are not. 

RDF interpretations:

The definitions of well-typed XML literal (strings) and XML values should
be tightened up.  In the definition ``XML value'' maps typed literals into
values; but in the semantic conditions ``XML value'' maps character strings
into values.  The definition is for ``well-typed XML literal string'', but
``well-typed XML literal'' is used as well, without a definition.


It is rather misleading to state that the only inconsistencies in
D-interpretations are ``datatype classes and assertions that ill-typed
literals are of type rdfs:Literal''.  There are other, closely related,
ways to produce inconsistency, such as  requiring "<br />^^rdf:XMLLiteral
to belong to ICEXT(I(rdf:XMLLiteral)).

Datatype entailment rules:

I do not believe that rule rdfd4 is valid.  I don't see how under the
current semantic rules for rdfs:subClassOf that one can infer an
rdfs:subClassOf relationship from just a subset relationship.

Appendix B:

The definition of subinterpretation is flawed.  Saying that
subinterpretation is defined in terms of triples, or even single-element
graphs, is different from defining subinterpretations in terms of graphs.
I suggest dropping the incorrect phrase that talks about triples.  

Subinterpretations do not need to be sub-structures.  To see this consider
interpretations that differ only in having extra elements of their domain,
i.e., domain elements that participate in no true triples.  These
interpretations will subinterpretations of each other, but there will be no
sub-structure relationship between them.

The paragraph about mappings between components of interpretations is
confusing.  What is a projection mapping?  What properties does it have?
What is the structure of an interpretation that needs to be preserved?  I
suggest dropping ``projection'' and ``preserves all the structure ...'',
and simply stating the requirement.

The proof of the Herbrand Lemma is not correct.  In the proof there is the
claim that ``if I satisfies E then I makes true all the triples that
Herb(E) makes true'', but this claim has not been shown.

The proof of the RDF Entailment Lemma is rather sloppy.  It refers to
``well-typed XML literal''

Translation to LBase:

Even the new version of LBase is inadequate as a target for a mapping from
RDF.  It leaves open several fundamental issues including the nature of
character strings.  Further, the inclusion of single quotes in LBase
strings is not possible, so there is no way of translating RDF literals
that contain single quotes.

Several aspects of the translation to LBase continue to be problematic.
There is no firm definition of NatNumber in LBase, so, for example, it
might be the case that rdf:Property(rdf-member(001)) , leading to problems
with URI references like rdf:_001.  The treatment of XML structures is
inadequate.  XML structures can have language tags,  which, by itself, may
not be a problem, but is an indication that insufficient care has been
taken in the definition of XML structures. There is no attempt to show that
all URIs can be used as names.

In addition to the above problems, the translation to LBase continues to be
incomplete.  For example, there is no axiom that makes all classes be
subclasses of rdfs:Resource.

Peter F. Patel-Schneider
Received on Sunday, 31 August 2003 13:55:34 UTC

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