W3C home > Mailing lists > Public > public-linked-json@w3.org > February 2013

Re: Blank Node Identifiers and RDF Dataset Normalization

From: Steve Harris <steve.harris@garlik.com>
Date: Mon, 25 Feb 2013 15:45:46 +0000
Cc: "'William Waites'" <ww@styx.org>, <msporny@digitalbazaar.com>, <public-rdf-wg@w3.org>, <public-linked-json@w3.org>
Message-Id: <13A03942-7B81-4D85-9F8A-944A2488BF82@garlik.com>
To: Markus Lanthaler <markus.lanthaler@gmx.net>
On 2013-02-25, at 13:00, Markus Lanthaler <markus.lanthaler@gmx.net> wrote:

>> For example:
>> 
>> SELECT * WHERE {
>>   ?g dc:date ?d .
>>   GRAPH ?g { ?x a foaf:Person }
>> }
> 
> Given that it has been decided that graph labels do *not* denote the graph,

I believe it would be more correct to say that graph labels do not HAVE to demote the graph, they're allowed to if you want them to.

Regardless, the example is valid regardless on whatever graph labelling semantics are being used - within some system with a known relationship between graph labels and metadata.

If the graph label refers to the document which was parsed, and the metadata refers to the parsing (which is a very common situation), then the example is equally valid.

I think you may be attaching too much important to the idea of denoting.

> I find such example especially confusing. You use the same variable (?g) in
> the subject position and as a graph label knowing that they do not refer to
> the same. Semantically, the two have nothing in common at all. ?g could
> denote a person, a document, an event, whatever. The graph ?g is a
> completely different "thing". Effectively you could say they use the same
> IRI by coincidence. I think it are these kind of examples that lead to the
> current situation. Contrast that with a query like and assume the IRI would
> denote the graph
> 
> SELECT * WHERE {
>   ?someone_thing :stated ?g .
>   GRAPH ?g { ?x a foaf:Person }
> }
> 
> 
> I think at the very least, the effects of the decision that graph labels do
> not denote the graph should be made clearer in RDF Concepts. I don't know
> how but maybe an example helps to illustrate the problem. That information
> also shouldn't be put in a non-normative note IMHO.

Well, first we'd have to find a problem with itů I suspect a world where graph labels always denote graphs would be much more confusing and counter-intuative to the average developer.

- Steve

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Steve Harris
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Received on Monday, 25 February 2013 15:46:17 GMT

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