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Re: Another try.

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 21 Feb 2012 15:43:37 -0600
Cc: public-rdf-wg@w3.org
Message-Id: <1D4C6BBB-A31D-486B-A58C-8E64371C01CA@ihmc.us>
To: Andy Seaborne <andy.seaborne@epimorphics.com>

On Feb 21, 2012, at 5:44 AM, Andy Seaborne wrote:

> 
> 
> On 21/02/12 07:56, Pat Hayes wrote:
>> For conservatives among us, the opposite re-interpretation is always
>> available. Any quad-graph can be thought of as a SPARQL dataset, by
>> 'slicing' the quads according to their last argument, and
>> re-declaring this parameter to be a graph label. However, to retain
>> the semantic flexibility (ie to have the triples in each graph able
>> to be re-interpreted differently in each labeled graph), we would
>> have to modify the RDF semantics to allow for this graph-local
>> context being involved in the truth recursions. And as already noted,
>> it is simpler, and much less of a change ot the basic RDF model,  to
>> do this by thinking of this construction in the quad-graph way as
>> being a set of property-with-three-argument quads rather than as a
>> collection of labelled sets of two-argument triples. And as so many
>> of the 'natural' uses of datasets seem to want to take advantage of
>> the apparent contextual' possibility of the graph label, and this
>> option is only available in a quad-store format in any case, it seems
>> comparatively harmless to attach the needed semantics directly to
>> this quad store format, rather than tinker with the semantics of
>> triples or try to make sense of graph 'names' which do not denote
>> graphs.
> 
> I was wondering about existing vocabularies.
> 
> If I understand the quad proposal, then all existing vocabularies are technically undefined because they never define P(S,O,G), only P(S,O).

No, that is fine. IEXT can be purely a set of triples in the new semantics, so every old interpretation is still a new interpretation. And that does "define" the value of P(S, O, G): its always flase, for any G. But in any case, RDF vocabularies are never *defined*, strictly speaking. They mean whatever their owner specifies them to mean. Right now, for example, any quad with a property in the rdf: or rdfs: namespaces is simply false, as a kind of default, but we are free to change this if we want to (without changing any of the triples, of course.) Actually I would recommend that we don't, since the rdf: and rdfs: vocabularies are not intended to be used 'contextually' (eg they dont change with time and should be resistant to subjective re-interpretation) so it would be good to restrict them to a purely triple-based meaningful use. Then writing something like 

G: { :A rdfs:subClass :B + } 

would be formally a contradiction (since that *quad* is defined to be false. because being a subclass isn't comething that you can put into a context. Or, we could decide it was, but then we would need to talk rather a lot about kinds of context and what effect they have on subclassing and so forth.) 

> 
> The graph-local context view seems to preserve the vocabulary by reinterpreting P(S,O).  It's less neat to have sets of triples + graph labels, but it does seem to carry-over existing data.

What I was trying to convey is that the graph-with-context view is formally identical with the quads view. What we have right now is graphs-without-context. 

> 
> Have I missed something?

Not sure (see above.)

Pat

> 
> 	Andy
> 
> 

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Received on Tuesday, 21 February 2012 21:44:15 GMT

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