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

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Thu, 11 Oct 2001 18:02:19 -0500
Message-Id: <p0510100cb7ebd1b75592@[205.160.76.193]>
To: Dan Connolly <connolly@w3.org>
Cc: w3c-rdfcore-wg@w3.org, pfps@research.bell-labs.com
>Pat Hayes wrote:
>>
>>  After getting this wrong several times,
>
>Now there's a red flag right there: the guy who has
>been doing symbolic logic for breakfast since about
>the time I was born got this wrong several times.

You could rephrase that as "the guy whose memory span is now too 
short to remember all his undergraduate math.."

>And even with all these contortions and special
>cases, RDF/XML 1.0 syntax *still* can't serialize
>all the graphs of this form.
>
>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.

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

>   --
>http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Oct/0140.html
>
>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?

>After thinking for a while[27Sep] about the question of whether
>the formalism for RDF graphs should be limited by RDF/XML 1.0
>syntax, I've come to the pretty firm conclusion that no,
>there's no reason we should have to redo the RDF Core model
>theory when we revisit the design of RDF syntax. In fact,
>this liberal abstract syntax should go a long way toward
>shaping the design of new RDF concrete syntaxes.

I agree.

>[27Sep]
>http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0420.html
>
>
>>  here's an attempt at a formal
>>  definition of an RDF graph. This is worded to make it align naturally
>
>"naturally". Hmm... that's a stretch!

Oh, come on, all you need to do is assign a bNode name to each blank 
node, and it's done. Could it be simpler?

Pat

PS> I would only put this style of definition in an appendix 
somewhere, just to keep the mathematicians happy. 99.9 % of the 
people who read the spec will be perfectly happy with the single word 
'graph'.

BTW, Seth Russell pointed out that some people take 'multigraph' to 
exclude loops, so its really a 'pseudograph'. I think I will just 
avoid ALL mathematical jargon.
-- 
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Received on Thursday, 11 October 2001 19:02:26 EDT

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