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Re: 2 RDFa SPARQL Test Harness Issues

From: Dave Beckett <dajobe@gmail.com>
Date: Sat, 17 May 2008 21:19:51 +0100
Message-ID: <8335bdf60805171319qc7a5367gd76ea5867d92cbfb@mail.gmail.com>
To: "Manu Sporny" <msporny@digitalbazaar.com>
Cc: "RDFa mailing list" <public-rdf-in-xhtml-tf@w3.org>, "Andy Seaborne" <andy.seaborne@hp.com>, "Benjamin Nowack" <bnowack@semsol.com>, "Dave Beckett" <dave@dajobe.org>

On Sat, May 17, 2008 at 7:53 PM, Manu Sporny <msporny@digitalbazaar.com> wrote:

<snip>

> ... but SPARQL.org, surprisingly says that there is a solution to the query.
>
> ----------------------------------------------------------------------
> ASK WHERE {
> _:a
>   <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
>      <http://xmlns.com/foaf/0.1/Person> .
> }
> ----------------------------------------------------------------------
>
> This leads me to believe that the SPARQL above doesn't do what we think
> it does, but I haven't been able to find any documentation detailing how
> bnode identification happens in SPARQL queries.

_:a is equivalent to an existential variable - "there exists a node
_a, such that ..."

> The question that we're attempting to ask above is "is there a bnode
> that has an rdf:type of foaf:Person?", not "is there any node that has
> an rdf:type of foaf:Person?".

For that you want.
 ASK WHERE {
 ?a
   <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
      <http://xmlns.com/foaf/0.1/Person> .
FILTER ISBLANK(?a)
}

I noticed this because I converted the sparql ASK WHERE to N-Triples
(via Turtle) and then did an rdf graph compare for runnign the rdfa
tests in raptor; there is no sparql interpretation involved.  I prefer
to have "less moving parts" in the testing, just an rdf parser and
graph compare.

Of course using Turtle for the results would not have this problem :)
(it supports UTF-8 like sparql, unlike N-Triples)

Dave
Received on Saturday, 17 May 2008 20:23:11 GMT

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