[Nepomuk] Re: counting literal values

[Sebastian Trüg]

Just a hunch: try adding Query::NoResultRestrictions to the
toSparqlQuery call.

Cheers,
Sebastian

On 12/01/2010 06:08 AM, Robby Stephenson wrote:
> Maybe I'm still missing something? The following code doesn't work for me:
> 
>   QUrl subject("http://example.com/subject");
>   QUrl property("http://example.com/number");
>   Soprano::LiteralValue value(1);
> 
>   Nepomuk::Resource res2(subject);
>   res2.addProperty(property, Nepomuk::Variant(1));
> 
>   Nepomuk::Query::ComparisonTerm term(Nepomuk::Types::Property(property),
>                                       Nepomuk::Query::LiteralTerm(value),
>                                       Nepomuk::Query::ComparisonTerm::Equal);
>   QString queryString = 
> Nepomuk::Query::Query(term).toSparqlQuery(Nepomuk::Query::Query::CreateCountQuery);
> Soprano::QueryResultIterator it = Nepomuk::ResourceManager::instance()-
>> mainModel()->executeQuery(queryString, 
> Soprano::Query::QueryLanguageSparql);
>   int cnt = it.next() ? it.binding(0).literal().toInt() : 0;
>   QCOMPARE(cnt, 1);
> 
> Robby
> 
> On Monday 29 November 2010, Sebastian Trüg wrote:
>> Hi Robby,
>>
>> your problem is that Nepomuk makes a few assumptions on the way the data
>> is stored[1]. You add a triple in the empty graph, thus it is ignored by
>> the query system.
>> You should rather use
>>
>> Nepomuk::Resource res( subject );
>> res.addProperty( predicate, value );
>>
>> Then your query will work. Using the model directly is discouraged. I
>> should actually add that to the API docs.
>>
>> This week I will start work on an API in between the Nepomuk::Resource
>> and the Model API allowing lower level data manipulations without having
>> to care about the format of the data beyond what you already did.
>>
>> Hope this helps,
>> Cheers,
>> Sebastian
>>
>> On 11/27/2010 08:09 AM, Robby Stephenson wrote:
>>> Hi All,
>>>
>>> I'm getting my feet a little wet with RDF and SPARQL, along with
>>> Nepomuk and Nepomuk Query.  One of my little test examples did not
>>> work qute as expected, so I was hoping someone might point out what I
>>> was doing wrong or where my incorrect assumption might be.
>>>
>>> I added a statement setting an example predicate property to a literal
>>> value. Then, I want to count the number of statements with that literal
>>>
>>> value. Here's what I tried first, which doesn't seem to work:
>>>   QUrl subject("http://example.com/subject");
>>>   QUrl predicate("http://example.com/number");
>>>   Soprano::LiteralValue value(1);
>>>   model->addStatement(subject, property, value);
>>>   Nepomuk::Query::ComparisonTerm
>>>   term(Nepomuk::Types::Property(predicate),
>>>   
>>>                                                                          
> Nepomuk::Query::Lit
>>>                                                                          
> eralTerm(value),
>>>                                                                          
> Nepomuk::Query::Co
>>>                                                                          
> mparisonTerm::Equal
>>>                                                                          
> );
>>>   
>>>   QString queryString =
>>>
>>> Nepomuk::Query::Query(term).toSparqlQuery(Nepomuk::Query::Query::Create
>>> CountQuery);
>>>
>>>   Soprano::QueryResultIterator it = model->executeQuery(queryString,
>>>
>>> Soprano::Query::QueryLanguageSparql);
>>>
>>>   it.next();
>>>   int count = it.binding(0).literal().toInt();
>>>
>>> I expect count to equal 1, since there is at least one matching
>>> statement in the model. But it equals 0. Looking at the query string,
>>> I see:
>>>
>>> select count(distinct ?r) as ?cnt where { ?r
>>> <http://example.com/number> ?v1 . ?v1 ?v2
>>> "1"^^<http://www.w3.org/2001/XMLSchema#int> . ?v2
>>> <http://www.w3.org/2000/01/rdf-schema#subPropertyOf>
>>> <http://www.w3.org/2000/01/rdf-schema#label> . graph ?v4 { ?r a ?v3 . }
>>> . { ?v4 a
>>> <http://www.semanticdesktop.org/ontologies/2007/08/15/nrl#InstanceBase>
>>> . } UNION { ?v4 a
>>> <http://www.semanticdesktop.org/ontologies/2007/08/15/nrl#DiscardableIn
>>> stanceBase> . } . }"
>>>
>>> Is it a problem with my use of Types::Property? Is there a better or
>>> "more correct" way to use the Query API to get a count of literal
>>> values?
>>>
>>> It works as expected if I hand-write the query as:
>>>
>>> select count(distinct ?r) as ?cnt where {
>>>
>>>   ?r <http://example.com/number>
>>>   "1"^^<http://www.w3.org/2001/XMLSchema#int>
>>>
>>> .
>>> }
>>>
>>> This is with KDE 4.5.3. Thanks!
>>> Robby
> 
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