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Re: need to determine what RDF is

From: Dan Connolly <connolly@w3.org>
Date: 30 May 2002 12:32:33 -0500
To: "Peter F. "Patel-Schneider <pfps@research.bell-labs.com>
Cc: danbri@w3.org, bwm@hplb.hpl.hp.com, www-rdf-comments@w3.org, em@w3.org, w3c-semweb-cg@w3.org
Message-Id: <1022779954.24872.142.camel@dirk>

On Thu, 2002-05-30 at 11:06, Peter F. Patel-Schneider wrote:
> From: Dan Connolly <connolly@w3.org>
> Subject: Re: need to determine what RDF is
> Date: 30 May 2002 10:31:43 -0500
> > On Thu, 2002-05-30 at 10:26, Peter F. Patel-Schneider wrote:
> > [...]
> > > I'm only interested in relationships between RDF graphs.  Which such
> > > relationships are RDF relationships?  
> > > 
> > > My view is that the only such relationships are RDF entailment and RDFS
> > > entailment.  Any agent that computes any other relationship between RDF
> > > graphs is not doing RDF.
> > 
> > Why is RDFS special? It's just the first of many RDF vocabularies,
> > no?
> No.
> RDFS is not an RDF vocabulary at all.  It is an extension to RDF, as
> witness its treatment in the RDF Model Theory document.

Sigh... terminology again... in what way is it not
an RDF vocabulary? You probably don't even know what I meant
by that term. What distinction do you mean to draw
between 'RDF vocabulary' and 'extension to RDF'?

> RDFS is special because RDFS entailment is defined in the same document as
> RDF entailment

Ah... then that's misleading; I worried about that.
I'll see that we split them into separate documents.

> and the RDF Schema document is being produced by the RDF
> Core Working Group.  

> > I could understand a definition that said 'anybody doing more than
> > RDF simple entailments isn't doing RDF', but I don't understand
> > a definition of RDF that includes RDFS but not dublin core,
> > RSS, DAML+OIL/OWL, etc.
> Then why is RDFS entailment in the RDF Model Theory document?

Editorial convenience.

>  Why is the
> RDF Schema document being produced by the RDF Core Working Group? 

For the same reason that the group that produced the C
standard also produced the C standard library: end-users
could write strstr(), but it's a pain; standardized
idioms promote interoperability.

And because we tried having them developed in separate
groups the first time around, and the communications
costs were very high.

> Why should RDF not include Dublin Core, RSS, DAML+OIL/OWL, etc?  Well,
> RDF can include any portions of these efforts that are expressible in RDF
> (by the simple expedient of including the RDF documents produced by these
> efforts).  However, RDF should not include any other portion of these
> efforts.  Why?  Well simply because these efforts are not part of RDF, as
> witness the fact that the RDF documents do not give them any special
> status.

Again, by analogy, the ANSI C WG doesn't have to write all
the C programs in the world.

You might say that the semantics of all those C progams
is specified by the C standard, while dublin core semantics
aren't actually expressed in RDF.
But consider C programs that do I/O withe external
devices and such.

I'm willing to stop saying that 'doing OWL is doing RDF',
but I need some term for the relationship between OWL
and RDF that is the same as the relationsihp between RDFS
and RDF, and the same as the relationship between
dublin core and RDF; as a placeholder, let's
call it an RDF watermelon.

An RDF watermelon is
  * a list of absolute URI references
	(usually, they share a prefix, for convenient use
	with XML namespace syntax)
  * an agreement that these terms may be used in RDF/xml
  * an agreement that when these terms are used in RDF/xml
    syntax, assertion of such a document licenses
    all simple entailments
  * a specification of further constraints on the
    meaning of these terms; i.e. more constraints
    on which interpretations are models.
    This specification may end up licensing
    further formal inferences, or it might just
    relate the terms to existing conventions and
    practices, in such a way that humans are
    expected to be able to judge which interpretations
    are models, but a machine's understanding
    will be incomplete.

RDFS, dublin core, and DAML+OIL look like RDF watermelons
to me.

> How could the situation be any different?  It seems that you are asking for
> W3C to bless any effort (e.g., DAML+OIL or KIF) that has any relationship
> to RDF, even if the only relationship is the effort uses URIrefs to
> identify its tokens.

Well, yes; that's pretty much what the Resource Description Framework
is, to me.

There are a few things beyond using URIrefs: monotonicity,
completeness (but not necessarily soundness) w.r.t.
simple entialment, the use of unicode strings (and XML
infosets) as literals. And for at least some period of time,
a willingness to use RDF/XML syntax for exchange.

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 30 May 2002 13:34:02 UTC

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