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Re: I have a trouble with The RDF Model

From: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
Date: Tue, 28 Nov 2000 20:04:44 +0100
Message-ID: <3A2401CC.77F8A82@bat710.univ-lyon1.fr>
To: pat hayes <phayes@ai.uwf.edu>
CC: RDF-Logic <www-rdf-logic@w3.org>
pat hayes wrote:
> Would it be
> possible for you, or someone connected with RDF, to give a precise
> specification of what exactly *is* the syntax of RDF?

My turn to try it :)
My understanding is that there are two levels of syntax in RDF.

The first level syntax is the XML-syntax proposed by the RDF recomendation. It is interpreted as a direct graph, whose nodes and arcs are labelled by URIs (or Literals for some nodes).
The semantic is (intended to be) quite trivial, and the syntax could very well be replaced by another one, as mentionned by Seth.

The second level syntax IS the direct labelled graph, and the RDF recomendation does not give any predefined semantics to it (that semantics depends on yet-to-describe schemas/ontologies).
That is *the* RDF syntax, as I understand it. The first level is only "serialization-oriented"...

Now, I said the RDF recomendation did not specify any second-level semantics, that is not absolutely true : the reification has an intended semantics to describe elements of the (second-level) language in the language itself.
Namely, some nodes of the graph (known as "reified statements") denote some arcs of the graph, so that the arcs themselves can be talked about.

<snip/>
> Now, does *that* have a model theory?

I'm affraid not...
There is actually a very hot debate on the RDF-interest mailing list,
which, as I am writing, I could formulate as :

"Do reified statements denote
 - the *interpretation* of a statement
   i.e. a semantic entity, which is unique and abstract,
or
 - the *expression* of a statement
   i.e. a syntactical entity, which could have many instances ?"

> The problem is that according to
> this rule, RDF names may refer to pieces of RDF syntax, so the
> language is highly self-referential.

This is the second hypothesis above, the one I favor, actually.
Sure, it makes it difficult to make a model theory of RDF,
but that is what will make RDF suited to the web, open as it is :
people will not only be able to annotate resources, but also annotated their annotations, to explain/justify/comment them.

  Pierre-Antoine
Received on Tuesday, 28 November 2000 14:37:08 UTC

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