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RE: The X Datatype Proposal

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Wed, 14 Nov 2001 20:38:51 +0000
Message-Id: <5.1.0.14.2.20011114200853.04531a40@joy.songbird.com>
To: Patrick.Stickler@nokia.com
Cc: w3c-rdfcore-wg@w3.org
At 08:20 PM 11/14/01 +0200, Patrick.Stickler@nokia.com wrote:
>Rather, we need
>
>    X foo _:1:"10" .
>    _:1 rdf:type xsd:integer .
>    Y foo _:2:"10" .
>    _:2 rdf:type xsd:byte .
>
>Now, we know which node is which and can rebuild
>our graph reliably.

Sure... I accept that.  It wasn't central to my point and I agree it has to 
be addressed in some way.

The current MT, being based on the abstract graph, doesn't have this 
problem because the graph nodes are self-identifying in this 
respect.  Which is fine as a basis for defining semantics. But, lacking a 
lexical serialization, means that we still need some way to present than 
(drawings of graphs or N-triples are our current candidates).

>My motivation for the X proposal notation was to try
>to get below the resource-centric graph and its
>relation to notations and capture the knowledge
>(statements) embodied in the graph.

Which, it seems to me is exactly what a formal semantics achieves.

>Again, it wasn't meant to be a notation, just a model,
>and to that end, I think it is simpler than the current
>graph model overall, once you take into account reification
>of statements.

I have come to a view that reification (at least as I see it's uses) 
doesn't need to be defined in the core of RDF.  To understand the formal 
semantics of RDF as Pat has defined it requires some effort of thought, 
mainly (IMO) to learn to think clearly about the distinction between syntax 
(tokens, inscriptions) and meanings (denotations, interpretations).  But 
beyond that, it really doesn't seem to me to be at all complicated.

> > And there are still all the issues of how to construct a
> > formal semantics
> > (preferably a model theory) for your proposal, which you
> > haven't started to
> > do.
>
>Nor will I, and if that is a prerequisite for consideration,
>then I guess that rules it out right there.

I think it is a prerequisite, because without a formal semantics everything 
else is built on sand.

> > Finally, I think there are some aspects of your proposal that
> > would prevent
> > it from describing some aspects of legal RDF as currently
> > defined
>
>That may be true, though I haven't yet seen any.
>
> > (notably
> > the distinction between subject nodes and nodes with URI
> > labels).
>
>Not at all. A subject node is a node which is the value of
>an SNode 'subject' facet. A node with a uri label is a UNode.
>
>The distinctions are quite explicit.

Quite.  In RDF, a node can both denote a statement *and* have a URI label:

     <rdf:Statement about="http://example.com/stmt">
       <rdf:predicate rdf:resource="http://example.com/pred" />
       <rdf:subject   rdf:resource="http://example.com/sub" />
       <rdf:object    rdf:resource="http://example.com/obj" />
     </rdf:Statement>

which corresponds to the triples:

     <http://example.com/stmt> rdf:type      rdf:Statement .
     <http://example.com/stmt> rdf:predicate <http://example.com/pred> .
     <http://example.com/stmt> rdf:subject   <http://example.com/sub> .
     <http://example.com/stmt> rdf:object    <http://example.com/obj> .

Your proposal seems to preclude this.

>So, I'm not really looking for the X proposal to be chosen
>over the others, necessarily, but perhaps the fact that it takes
>so different a view may be useful in understanding and evolving
>the other proposals. Then again, maybe not...

Well, yes, I have in the past found it useful to think about RDF in terms 
of reified statements.  (e.g. 
http://public.research.mimesweeper.com/RDF/RDFContexts.html.)  But I have 
always seen any such view as being underpinned by the basic RDF triple 
model, rather than vice versa.

It was not previously clear to me that you were not promoting this as an 
alternative approach to handling datatyping of literals.  I suppose that, 
at this stage of the working group life, we are really trying to converge 
on some common concepts to present to the world.

#g


------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
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Received on Wednesday, 14 November 2001 16:09:43 EST

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