[Nepomuk] Some issues on current master

[Marco Martin]

On Thursday 31 May 2012, you wrote:
> On Thursday 31 May 2012, Sebastian Trüg wrote:
> > please see if this patch fixes the issue.
> > 
> > On 05/31/2012 10:24 AM, Marco Martin wrote:
> > > On Thursday 31 May 2012, Marco Martin wrote:
> > >> On Thursday 31 May 2012, Sebastian Trüg wrote:
> > >>> which version of virtuoso are you using?
> > >>> 
> > >>> And, yes, the virtuoso branch needs to be merged in kdelibs indeed.
> > >> 
> > >> i tried on 2 different systems with 6.1.2 and 6.1.4, now i'm trying to
> > >> install 6.1.5
> > > 
> > > with 6.1.5 apparently there is the same issue of parse error (syntax
> > > error at exists)
> 
> now the query is actually executed, but a query like
> 
> select distinct ?r ?reqProp1 where { { OPTIONAL { ?r
> <http://www.semanticdesktop.org/ontologies/2007/01/19/nie#url> ?reqProp1 .
> FILTER(bif:exists((select (1) where { ?r a [
> <http://www.semanticdesktop.org/ontologies/2007/08/15/nao#userVisible>
> "true"^^<http://www.w3.org/2001/XMLSchema#boolean> ] . }))) . } }
> 
> (similar to what the query api tends to generate now)
> just spikes the cpu usage of virtuoso and will never finish

something like

select distinct ?r ?reqProp1 where {?r ?v1 ?v2 . FILTER(bif:exists((select (1) 
where { ?r a [ 
<http://www.semanticdesktop.org/ontologies/2007/08/15/nao#userVisible> 
"true"^^<http://www.w3.org/2001/XMLSchema#boolean> ] . }))) . }

seems to work.

however, with the query api if you do something like

m_query.addRequestProperty(Nepomuk::Query::Query::RequestProperty(NIE::url()));

to have some properties already in the result to minimize round-trips, the 
generated query becomes as the one i put before,
 select distinct ?r ?reqProp1 where { { OPTIONAL { ?r
 <http://www.semanticdesktop.org/ontologies/2007/01/19/nie#url> ?reqProp1 .
 FILTER(bif:exists((select (1) where { ?r a [
 <http://www.semanticdesktop.org/ontologies/2007/08/15/nao#userVisible>
 "true"^^<http://www.w3.org/2001/XMLSchema#boolean> ] . }))) . } }

with one filter clause inside each OPTIONAL block, and this seems to kill 
virtuoso (6.1.5 on this machine now)

Cheers,
Marco Martin