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Re: Active issue rdfms-graph; formal description of properties ofan RDF graph

From: Dan Connolly <connolly@w3.org>
Date: Sat, 20 Oct 2001 09:43:08 -0500
Message-ID: <3BD18D7C.9F5FED05@w3.org>
To: Pat Hayes <phayes@ai.uwf.edu>
CC: w3c-rdfcore-wg@w3.org, pfps@research.bell-labs.com
[It seems that folks have taken the lack of a reply
from me as agreement; not so...]

Pat Hayes wrote:
> >I suggest, again, the following simple abstract syntax:
> >
> >   An RDF graph is a set of triples <S, P, O>; each
> >   of S, P, O is a term; a term is either an absolute
> >   URI reference, a bNode, or a literal.
> >   --
> >http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Oct/0140.html
> >
> Well, I'm happy to go along with the more liberal labelling rules, to
> be sure. These restrictions only make life more complicated by the
> need to avoid exceptional cases in the model theory, closure rules,
> etc.. (One of the reasons why I laid out all those conditions on N
> and E labels was to make it easy to erase them one at a time :-)
> But this abstract syntax is really just N-triples,

It's very close to N-triples... that is: N-triples is designed
to closely model this abstract syntax, yes...

> and I prefer to
> keep the graph as a separate entity.

This sort of graph is separate. N-triples syntax is a BNF sort
of thing: the statements are ordered; there's whitespace
and punctuation, etc. bNodes have a particular
syntactic representation, etc. In the graph formalism
I'm suggesting, the only thing we specify about
bNodes is that they're different from absolute
URI references and literals.

> >The model theory straightfowardly applies to this liberal
> >syntax, I believe. Regarding scope, I think it's straightforward
> >to treat bNodes the way local variables are treated in
> >traditional logical syntax: you rename them as necessary
> >when you merge graphs.
> Yes, it CAN be done that way. I think its uglier, and also it is kind
> of cheating, since right now we don't have anything in RDF syntax
> (not even in Ntriples) to specify the 'document' boundary. And
> remember how much trouble we had with this at the F2F?

Yes, we do have something in RDF synatax and in n-triples
to specify the document boundary: the document boundary


We don't have a way of putting two scopes
into one document, but that's by design
(or: by design limitation, as one of our issues suggests).

And no, I don't remember how much trouble we had with
this at the F2F; I wasn't there the 2nd day. The
previous model theory, which was based on n-triples
concrete syntax, worked just fine for me.

Let me review the record of the 2nd day...

It seems to come down to this:

  Pat: the realization that I have, if I do the MT as attached
  to the graph, then issues like scope of exist quant
  go away becauset there are no scopes in the graph.


If you substitute "set of triples..." as above
for graph, the epiphany holds, no?

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Saturday, 20 October 2001 10:43:12 UTC

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