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Re: Closing rdfms-difference-between-ID-and-about (was: RDFCore WG minutes for the telecon 2001-10-12)

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Tue, 23 Oct 2001 17:18:32 -0500
Message-Id: <p05101049b7fb999409af@[205.160.76.193]>
To: Dan Connolly <connolly@w3.org>
Cc: w3c-rdfcore-wg@w3.org
>Brian McBride wrote:
>[...]
>>     o Pat seems to reckon the model theory is simpler with a set. 
>>Can we extend
>>  the notion of a tidy graph so that it removes duplicate 
>>statements.  Any untidy
>>  graph has an equivalent tidy graph, and the model theory is 
>>defined in terms of
>>  that.
>
>You seem to be discussing this as if issue #rdfms-graph
>were to be resolved as per the Sep model theory WD.
>
>Please see my 11 Oct suggestion to replace it wholesale, which
>was greeted with at least two voices of support:
>
>http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Oct/0186.html

Well, since you bring it up, let me add a voice of nonsupport, for 
several reasons.

1. The apparent simplicity of the definition is largely only 
apparent, since we have to give the rules for how to understand such 
a set of triples as a graph. There are many ways to do it, and the 
only way to be precise is to say what counts as a graph and to give 
the mapping between the triples syntax and the graph. ( Even if you 
want to just trash the graph, the same basic issues come up. Do we 
count two different occurrences of the same literal in two triples as 
being 'really' the same (tidyness on literal nodes) or not? Etc.  If 
these issues are not resolved in the syntax description they will 
just come up again, more awkwardly, in the MT itself; the statements 
of entailment will start to get complicated because they will have to 
distinguish free and bound symbols, and so on.)

2.  As stated it isn't workable. We cannot have 'blank properties' 
since there would be no way to know which arcs belonged to which 
properties. The use of nodeID-style labels in the graph really would 
require that these nodeIDs become incorporated into the core RDF 
syntax. We could do that, but it seems like a big step to take, and I 
hope that Frank would object to it as creeping syntaxism. (This is 
purely a syntax issue, but I think it is important.)

3. Allowing literals on property arcs seems pointless. (The MT could 
handle it, but unless some datatyping scheme assigns property 
extensions, any triple with a literal property would be automatically 
false in every interpretation.)


On the other hand, I would suggest that we could go *some* way to 
liberalizing the syntax. In particular, I can see no rational reason 
for forbidding literals from the subject position, and lots of very 
good reasons to permit it, particularly when we consider literal 
datatyping.

Pat
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Received on Tuesday, 23 October 2001 18:36:50 EDT

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