Hi,
I am trying to build the following query using ARQ
PREFIX ldp: <http://www.w3.org/ns/ldp#>
CONSTRUCT
{
?a ldp:member ?b .
}
WHERE {
SELECT ?b WHERE {
GRAPH ?d {
?b ldp:memberOf ?a
}
GRAPH ?b {
?r ldp:memberOf ?s
}
}
}
I was able to create the patterns and Ops necessary for the building
But when it comes to building the construct operation, which I created with
OpAsQuery and then setting the construct type, I was not able to add the
inner select since there is no OpSelect for that purpose.
My code in Scala
val resourceVar = Var.alloc("b")
val provenanceVar = Var.alloc("d")
val containerVar = Var.alloc("a")
val memberOf = NodeFactory.createLiteral("ldp:memberOf")
val member = NodeFactory.createLiteral("ldp:member")
val provenanceGraphPattern = new BasicPattern()
provenanceGraphPattern.add(new Triple(resourceVar, memberOf, containerVar))
val provenanceBGP = new OpBGP(provenanceGraphPattern)
val resourceGraphPattern = new BasicPattern()
resourceGraphPattern.add(new Triple(Var.alloc("r"),
NodeFactory.createLiteral("ldp:memberOf"), Var.alloc("s")))
val resourceBGP = new OpBGP(resourceGraphPattern)
val provenanceGraph = new OpGraph(provenanceVar, provenanceBGP)
val resourceGraph = new OpGraph(resourceVar, resourceBGP)
val join = OpJoin.create(provenanceGraph, resourceGraph)
val innerSelect = OpAsQuery.asQuery(join)
innerSelect.addResultVar(resourceVar)
val subQuery = new ElementSubQuery(innerSelect)
val constructPattern = new BasicPattern()
constructPattern.add(new Triple(containerVar,
member,
resourceVar
))
val op = Algebra.compile(subQuery)
val result = OpAsQuery.asQuery(op)
result.setConstructTemplate(new Template(constructPattern))
result.setQueryConstructType()
result.getPrefixMapping
.setNsPrefix("ldp", "http://www.w3.org/ns/ldp#";)
result
*This creates the following query, which lacks of the inner SELECT clause*
PREFIX ldp: <http://www.w3.org/ns/ldp#>
CONSTRUCT
{
?a "ldp:member" ?b .
}
WHERE
{ GRAPH ?d
{ ?b "ldp:memberOf" ?a }
GRAPH ?resource
{ ?r "doc:encodes" ?s }
}
Any help is appreciated
*PS*: Also, which is the way to create a prefix reference Node in the
Triple. NodeFactory.createLiteral seems to add "" always and
NodeFactory.createURI always adds <>
Regards,
Guillermo.
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