Query execution fails in Jena

[timmy....@gmail.com]

Hi,

I'm trying to execute the following (simplified) query via Jena, but it fails. It works fine in the admin console though, so the problem seems to be in the Jena layer.

PREFIX : <http://www.semanticweb.org/dummy#>
SELECT (<_:bnode__...> as ?s) ?a ?b ?c
FROM <http://a.named.gaph>
WHERE {  
    <_:bnode__...> a :Something; :pred_a ?a ; :pred_b ?b .
 OPTIONAL { <_:bnode__...> :pred_c ?c }    
}

The exception:

com.hp.hpl.jena.sparql.ARQException: com.complexible.stardog.StardogException: Encountered " <BLANK_NODE_LABEL> "_:b0 "" at line 3, column 10.

When I leave the subject section out of the SELECT clause, it fails with a different exception.

So

PREFIX : <http://www.semanticweb.org/dummy#>
SELECT ?a ?b ?c
FROM <http://a.named.graph>
WHERE {  
    <_:bnode__...> a :Something; :pred_a ?a ; :pred_b ?b .
 OPTIONAL { <_:bnode__...> :pred_c ?c }    
}

returns

com.complexible.common.rdf.query.parser.sparql.ast.VisitorException: BNodeID already used in another scope: b0

I'd appreciate some feedback. Thanks.

[Michael Grove]

Can you provide the actual query that fails to parse?

Cheers,

Mike

 

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[Evren Sirin]

The <_:bnode> syntax is non-standard and is not supported through the
Jena interface of Stardog. The main reason for this is when you call
`Query.create(String).toString()` in Jena, the special bnode in the
query string turns into a regular bnode in the output string. There
are various restrictions for regular bnodes in SPARQL which causes the
errors you see.

The workaround would be to use a variable in the query and then a
filter like this:

FILTER (STR(?s) = "bnode__...")

Note that, there is no preceding "_:" when STR is applied to a bnode in Stardog.

Best,
Evren