What's queryFor( sg )?
It is possible to construct, programmatically, bad queries. These might
result in legal strings (but a different query).
Scala's fine but please provide a complete, minimal example.
TDB has an in-memory version for easy testing. It uses all the TDb
machinery, just has RAM-based disk storage (and it's slow - it copies a
lot to get true semantics).
The dots don't change the semantics but if you see them after
Query.toString, then you proably have a constructed query that is bad.
Andy
On 05/08/11 18:33, Svatopluk Šperka wrote:
Hi,
I am using Jena's TDB as a storage for data from my analysis. I use
jena.update.GraphStore to access it because I have to modify contained quads
beside adding them. Now, I have this problem that I need to find a graph in TDB
with a query that is built by using constructs from jena.sparql.syntax. But I
can't.
The curious and important fact is that if I take that constructed query and
transform it into a string and create a new query object from this string, it
works. The following code does not show that exactly - I've assigned the value
of query.toString from previous run to the variable query1.
In scala it looks like this:
println( graphStore.toString )
val query = queryFor( sg ) // this constructs a query by using
jena.sparql.syntax
val query1 = QueryFactory.create( "SELECT ?g WHERE { GRAPH ?g { ?v1<http://t.st#p1> ?v2
. FILTER notexists {?s ?p ?o . FILTER ( ( ?s != ?v1 ) || ( ( ?p !=<http://t.st#p1> ) || ( ?o
!= ?v2 ) ) ) } }}" ) // the exact same query created from string
println( "query:\n"+query.toString( jena.query.Syntax.syntaxSPARQL_11 ) )
println( query1.toString( jena.query.Syntax.syntaxSPARQL_11 ) )
val plan = QueryExecutionFactory.createPlan( query, graphStore )
val plan1 = QueryExecutionFactory.createPlan( query1, graphStore )
val result = plan.iterator
val result1 = plan1.iterator
println("hasNext built query: "+result.hasNext+" from-string query: "+
result1.hasNext )
Output of this part of the script when run:
// contents of the graphStore
(dataset
(graph
(triple<http://fit.vutbr.cz/qa#g-1> <http://fit.vutbr.cz/qa#t> 1)
)
(graph<http://fit.vutbr.cz/qa#g-1>
(triple _:-5e688aa4:1319ac49d09:-7ffe<http://t.st#p1>
_:-5e688aa4:1319ac49d09:-7ffd)
))
// string representation of built query
query:
SELECT ?g
WHERE
{ GRAPH ?g
{ ?v1<http://t.st#p1> ?v2 .
FILTER notexists {?s ?p ?o .
FILTER ( ( ?s != ?v1 ) || ( ( ?p !=<http://t.st#p1> ) || ( ?o !=
?v2 ) ) )
}
}}
// string representation of from-string query (dots after triple patterns are
missing … ? )
SELECT ?g
WHERE
{ GRAPH ?g
{ ?v1<http://t.st#p1> ?v2
FILTER notexists {?s ?p ?o
FILTER ( ( ?s != ?v1 ) || ( ( ?p !=<http://t.st#p1> ) || ( ?o !=
?v2 ) ) )
}
}
}
hasNext built query: false from-string query: true // built query has not
found a match, from-string query has
Right now, I'm sidestepping the problem by doing QueryFactory.create( queryFor(
sg ).toString( jena.query.Syntax.syntaxSPARQL_11 ) ), i.e. by converting a
query to string and back to query - and it works. That shows that there is a
problem somewhere in the jena.sparql.syntax, probably.
If there is a better way to programmatically construct queries, please give me
a clue. However, I would like to avoid algebra because it's kind difficult for
me to imagine complex queries in it - but if there is not another way then I
will fight ;)
Anyway, I'm pretty sure that there's a bug somewhere and I'm definitely not
satisfied with the current solution so I'll be more than happy to help (but I
can't provide the whole source code).
Thank you very much in advance !
Regards,
Svatopluk Šperka
