[Mulgara-general] empty results from SPARQL queries

Mark Stubbeman MStubbeman at algebraixdata.com
Fri Feb 3 18:04:16 UTC 2012


Here's the Dumper() print of the query before I execute it:

$VAR1 = bless( {
                 'query' => 'SELECT DISTINCT ?s WHERE { ?s ?p ?o . }',
                 'error' => undef,
                 'useragent' => undef,
                 'results' => []
               }, 'RDF::Query::Client' );

I get the feeling I may be relying upon defaults which work with one DB but not the other.  Since I'm new to this I'm not able to pick it out though.

Thanks,
Mark

-----Original Message-----
From: mulgara-general-bounces at mulgara.org [mailto:mulgara-general-bounces at mulgara.org] On Behalf Of Paul Gearon
Sent: Friday, February 03, 2012 10:11 AM
To: Mulgara General
Subject: Re: [Mulgara-general] empty results from SPARQL queries

Mulgara usually works fine with HTTP, so I'm not sure.

Would you be able to get a copy of the HTTP request for this please?
That may contain a clue.

Thanks in advance.

Paul

On Fri, Feb 3, 2012 at 10:21 AM, Mark Stubbeman <MStubbeman at algebraixdata.com> wrote:
> I'm new to SPARQL and to triple-store technology in general.  I have a 
> couple of example DBs - Mulgara being one of them - against which I am 
> trying to write some simple Perl code to submit queries and extract 
> responses.  The following works against one of my DB's but not against
> Mulgara:
>
>
>
> sub runQuery
>
> {
>
>   use RDF::Query::Client;
>
>
>
> # $webURL scrubbed of actual hostname but otherwise true to my actual 
> code
>
>   my $webURL = "http://$somehostname:8080/sparql";
>
>
>
> # an array of lines read from a file containing a SPARQL query
>
>   my @queryIn = @_;
>
>   my $funcQuery = join('', @queryIn);
>
>
>
>   print "Query\n-----\n\n$funcQuery\n";
>
>   my $query = RDF::Query::Client->new($funcQuery);
>
>   my $iterator = $query->execute($webURL);
>
>   print "Response\n------\n\n";
>
>   print Dumper($iterator);
>
>   while (my $row = $iterator->next)
>
>   {
>
>     print "$row\n";
>
>   }
>
> }
>
>
>
> With $webURL directed at another DB we get the following:
>
>
>
> Executing: C:\sandboxes\cdbms\Hawk\Tests\SP2Bench\queries\q1.sparql
>
>
>
> Query
>
> -----
>
>
>
> SELECT DISTINCT ?s WHERE { ?s ?p ?o . }
>
> Response
>
> ------
>
>
>
> $VAR1 = bless( {
>
>                  '_peek' => [],
>
>                  '_row' => undef,
>
>                  '_count' => 0,
>
>                  '_type' => 'bindings',
>
>                  '_finished' => 0,
>
>                  '_names' => [],
>
>                  '_args' => {},
>
>                  'sorted_by' => [],
>
>                  '_stream' => sub { "DUMMY" },
>
>                  '_open' => 0
>
>                }, 'RDF::Trine::Iterator::Bindings' );
>
> { s=<http://localhost/publications/articles/Journal1/1944/Article4> }
>
>
>
> (note that the output has been truncated to just one line).  However, 
> with $webURL set to our Mulgara installation the same code generates 
> the
> following:
>
>
>
> Query
>
> -----
>
>
>
> SELECT DISTINCT ?s WHERE { ?s ?p ?o . }
>
> Response
>
> ------
>
>
>
> $VAR1 = bless( {
>
>                  '_peek' => [],
>
>                  '_row' => undef,
>
>                  '_count' => 0,
>
>                  '_type' => 'bindings',
>
>                  '_finished' => 0,
>
>                  '_names' => [
>
>                                's'
>
>                              ],
>
>                  '_args' => {},
>
>                  'sorted_by' => [],
>
>                  '_stream' => sub { "DUMMY" },
>
>                  '_open' => 0
>
>                }, 'RDF::Trine::Iterator::Bindings' );
>
>
>
> We get back an iterator (with slightly different properties) but no 
> results.  I know via the Mulgara webui that the data is there.  That's 
> how I load the data.  I'm not sure what to use for Graph URI (several 
> settings seem to work) but for the above exercise I used "<hostname>:8080/sparql"
> where <hostname> is the same as $somehostname from the sample code.
>
>
> _______________________________________________
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> Mulgara-general at mulgara.org
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>
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