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Re: Issues danc-01 Re: 2 formalities in RDF concepts

From: Dan Connolly <connolly@w3.org>
Date: Mon, 03 Feb 2003 16:46:48 -0600
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
Message-id: <1044312407.13420.106.camel@dirk.dm93.org>

On Mon, 2003-02-03 at 16:13, pat hayes wrote:
[...]
> There are really two ways to go. We can say that RDF syntax (I'll 
> avoid the G-word for now) uses identifiers for blank nodes somehow; 
> or not, ie blank nodes are blank. If we go the first way, then the 
> concept of 'same graph' is effectively useless, since a graph with a 
> systematic change to its bound variables is semantically 
> indistinguishable from the original; and we have to talk everywhere 
> about equivalence classes of graphs, in effect, or isomorphism 
> between graphs. Also there are issues about scopes of these bound 
> variables, which we put to bed 18 months ago and which it would be a 
> chore, to put it mildly, to re-open at this stage. We decided in 
> Sebastopol to go the second route, ie to identify graphs with 
> indistinguishable blank nodes and to therefore not bother with 
> notions of renaming, bound variable and so on.

Yes, that's the issue as I see it.

> My own preference is that we retain the advantages of this second way 
> of doing things and re-write the concepts document wording to reflect 
> the decisions we made in Sebastopol and which we have been using as a 
> basis for our discussions ever since.

OK by me. That was my understanding when I sent the comment
that resulted in danc-01.

I didn't realize we could trace it to a WG decision but upon
review, it's pretty clear from the record:

"It was agreed that Pat would update the model theory based on the graph
instead of n-triples."
 -- http://www.w3.org/2001/sw/RDFCore/20010801-f2f/

Jan? Jeremy? Graham? Others? What say you?


> >Also, add graph to the list of terms imported from concepts.
> >[[
> >We use the following terminology defined there: uriref, literal, plain
> >literal, typed literal, blank node and triple.
> >]]
> 
> I am willing to do this IF the concepts doc is rewritten to say 
> clearly and unambiguously that an RDF graph *is* a set of RDF 
> triples, rather than any kind of 'graph' in any sense from 
> mathematical graph theory. Otherwise I would prefer that the 
> definition in the concepts document be replaced with a reference to 
> the semantics document.
> 
> >I do think the term "Graph Equality" is misleading; I'd prefer
> >Graph Equivalence for the RDF Concepts heading.
> 
> I disagree. If we stick to our guns here, we really do mean graph 
> equality. It is up to us to define 'graph' so that equality comes out 
> right, and we know how to do that.
> 
> We have had this worked out now for a very long time. Why screw it up 
> at this stage?
> 
> Pat
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Monday, 3 February 2003 17:47:27 EST

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