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Re: RDFCore WG: Datatyping documents

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 04 Feb 2002 15:45:51 -0500
To: patrick.stickler@nokia.com
Cc: www-rdf-logic@w3.org
Message-Id: <20020204154551T.pfps@research.bell-labs.com>
From: Patrick Stickler <patrick.stickler@nokia.com>
Subject: Re: RDFCore WG: Datatyping documents
Date: Mon, 04 Feb 2002 22:03:06 +0200

> On 2002-02-04 20:43, "ext Peter F. Patel-Schneider"
> <pfps@research.bell-labs.com> wrote:
> 
> > From: Patrick Stickler <patrick.stickler@nokia.com>
> > Subject: Re: RDFCore WG: Datatyping documents
[...]
> > Date: Mon, 04 Feb 2002 20:18:24 +0200
> > The problem mentioned above has everything to do with the
> > denotation of Unicode nodes, and nothing to do with multiple or
> > non-canonical lexical forms.
> 
> Fair enough. I take this to mean that whether or not the mapping
> from a Unicode node to a value is N:1 or 1:1 is irrelevant so
> long as it is not N:N or 1:N, right?

I guess not, but I'm not sure what you are getting at.   In a single
datatype the mapping is N:1 or 1:1, but with multiple datatypes it would be
N:N, which is the problem.  

[...]

> > Well, yes, and that may be consistent with the diagrams in the TDL
> > document, but the diagrams don't really say how any of that works, so we
> > are left only with the model theory.  A simple example of how TDL works in
> > practice, with an example like
> > 
> > age rdfs:range xsd:integer .
> > John age "10".
> 
> In this example, which is using the global/implicit
> idiom, you have a literal "10" which may be interpreted
> as a member of the lexical space xsd:integer. Thus,
> we have a TDL pairing ("10", xsd:integer). This pairing,
> given the MT definitions of datatypes -- namely that
> a datatype has a lexical space, a value space, and an
> N:1 mapping from the lexical space to the value
> space -- unambiguously denotes the mapping ("10", 10).
> 
> Now, if we take the local/explicit idiom
> 
>    John age _:1 .
>    _:1 rdf:value "10" .
>    _:1 rdf:type xsd:integer .
> 
> again we have the literal "10" and again the same TDL
> pairing ("10", xsd:integer) which denotes the mapping
> ("10", 10).
> 
> Insofar as the graph syntax is concerned, "10" is just
> a literal (a Unicode node). It is the context of the
> datatype, provided by the global or local idiom, that
> defines the TDL pairings that are the basis for
> interpretation.

Yes, but what *is* the interpretation?

I've been expecting something like:

	In TDL a single URL is used to refer to a datatype.  Bound up in
	the datatype is a mapping from lexical forms to their values.

	The meaning of a Unicode node in TDL is a data value, as above, not a
	lexical form.  The data value for a Unicode node is, however,
	determined by a mapping for some datatype.  The datatype mapping to
	use comes from ..........

	One way to determine the datatype mapping used is by the ``global''
	idiom, usually using rdfs:range on a property, as follows

		age rdfs:range xsd:integer .

	which specifies that objects of age triples in an RDF graph are to
	be given meaning according to the mapping from Unicode strings to
	integers defined by xsd:integer (the XML Schema integer datatype).

	Thus

		John age "10" .

	taken together with the above statement, means that the age of John
	is the integer 10, and not the Unicode string "10", or the pair
	<"10",10>, or some other thing.  The MT for TDL reflects this
	directly, not through any indirection.

Now I'm not saying that the wording above can actually be turned into an
actual datatype scheme for RDF.  I'm just saying that the TDL document
desperately needs something like this to give some intuitions to the
pictures and model theory.

[...]

> > If you do not,
> > then I expect you to retract the TDL document as it now stands.
> 
> Although I sincerely value your opinion and input a great
> deal, even if I did not agree with you (which I think I do),
> I would not have retracted the TDL proposal, per se, but rather
> continue to support the refinement/correction of its MT.

The trouble is that the TDL document is very specific in what it says.
(And, by the way, that is one of the reasons to have a MT or other
well-specified semantics.)  Right now the document says that the meaning of
Unicode nodes are pairs consisting of Unicode strings and data values.
Without quick, clear, and forceful statements to the contrary, TDL will be
inextricably associated with this meaning,.

> All of the proposals are works
> in progress, and all have issues to be addressed. We are not
> allowing only "perfect" and "pristine" proposals to remain on the
> table for discussion and consideration. RDF Core is after all, a
> *working* group, no? ;-)

Yes, but that doesn't give anyone license to contradict themselves and thus
confuse others, which is the situation that I think you are finding
yourself in.  (Yes, not by intent, and maybe unknowingly, but I think that
readers deserve to be told what is going on.)

> Cheers,
> 
> Patrick

Peter F. Patel-Schneider

PS:  We all are guilty now and then of emitting statements and/or documents
that give others false impressions of our stances.  However, I believe that
we should all take extraordinary efforts to fix such false impressions.
Received on Monday, 4 February 2002 15:47:50 GMT

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