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

RE: Blank Node Identifiers and RDF Dataset Normalization

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Mon, 25 Feb 2013 14:00:45 +0100
To: "'Steve Harris'" <steve.harris@garlik.com>, "'William Waites'" <ww@styx.org>
Cc: <msporny@digitalbazaar.com>, <public-rdf-wg@w3.org>, <public-linked-json@w3.org>
Message-ID: <00d301ce1358$2275ac30$67610490$@lanthaler@gmx.net>
> 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 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.


--
Markus Lanthaler
@markuslanthaler
Received on Monday, 25 February 2013 13:01:19 GMT

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