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Re: "the graphs referred to in the FROM clauses" [comment: major technical: underspecified errors]

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 13 Jan 2006 12:01:12 -0600
Message-Id: <p06230901bfed97b7e89d@[10.100.0.23]>
To: Dan Connolly <connolly@w3.org>
Cc: public-rdf-dawg@w3.org

>In "major technical: underspecified errors"
>http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2006Jan/0066.html
>
>we find...
>
>>  Also in this section,
>>  there is no mention of any syntax or runtime checks that an IRI
>>  actually identifies a graph.  Possibly the interpretation of an IRI that
>>  does not identify a graph is that the graph is empty.  However, this would
>>  be a disservice to the user since it would not alert the user to
>>  a typo in spelling a graph IRI.  It would be better to specify an error.

I agree with that observation, FWIW.

>  > Presumably the list of acceptable IRIs would be implementation-defined.
>
>I was going to say that this is covered by this text:
>
>[[
>The FROM NAMED syntax suggests that the IRI identifies the 
>corresponding graph,
>but actually the relationship between a URI and a graph in an RDF 
>dataset is indirect.
>the IRI identifies a resource, and the resource is represented by a graph
>(or, more precisely: by a document that serializes a graph).
>For further details see [WEBARCH].
>]]

Blech. The identified resource is represented by a graph? Surely it 
should be the other way round. The resource is something like an 
XML/RDF document source (right?) and that Webarch-represents 
(indicates/describes/is a lexicalization of/whatever) the graph, not 
what is represented BY the graph.

But in any case, seems to me that the useage of "resource" and 
"represent" in [WEBARCH] has always been so loose and scruffy 
(presumably with intent) that it would be quite in order to assert 
that the RDF graph itself was the "resource", and that what you get 
when you HTTP it is a "representation" of this "resource". If a 
Webcam can supply a representation of the street it is pointing at, 
which therefore counts as a "resource", then why can't a graph be a 
resource? (OK, OK, this isn't the right forum to be raising these 
issues. Grumble grumble, mutter mutter.)

>
>but now I'm not so sure.
>
>In 9 Specifying RDF Datasets...
>
>[[
>The dataset resulting from a number of FROM and FROM NAMED clauses is:
>
>       * a default graph consisting of the merge of the graphs referred
>         to in the FROM clauses
>       * a set of (IRI, graph) pairs, one from each FROM NAMED clause.
>]]
>
>we refer to "the graphs referred to in the FROM clauses". I wonder
>if that's coherent... hmm...

Well, are we clear on what we meant it to mean? If so, its just a 
matter of finding the right words. Can we speak of the merge of a 
graph and a named graph? Hmm, I guess so, if we can have a set of 
triples mixed with quads. I'm not sure that we have a name for such a 
thing, though.

Why do we want to keep the names attached to the FROM NAMED graphs? 
Can a query variable bind to the name of a graph in the dataset? If 
so, we need to re-write the basic definitions to allow for this.

Pat


>
>
>--
>Dan Connolly, W3C http://www.w3.org/People/Connolly/
>D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E


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Received on Friday, 13 January 2006 18:01:22 GMT

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