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https://issues.apache.org/jira/browse/JENA-2020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17257345#comment-17257345
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Martin Pekár commented on JENA-2020:
------------------------------------
{{The executor for OpExistence is seen below:}}
{code:java}
protected QueryIterator execute(OpExistence opExistence, QueryIterator input) {
OpBGP bgp = new OpBGP(BasicPattern.wrap(opExistence.getCoveringTriples()));
QueryIterator coveringIter = exec(bgp, input);
Triple checkTriple = opExistence.getCheckTriple().getTriple();
while (coveringIter.hasNext())
{
checkTriple = TripleConretise.concretiseTriple(checkTriple,
coveringIter.nextBinding());
}
return checkTriple.isConcrete() ? exec(opExistence.getBGPNotReordered(),
input) : emptyIterator();
}{code}
The call to checkTriple.isConcrete() is true in all tests. The call to exec in
the third line would return a new iterator, which I iterate. But on the last
line, I return a new iterator with the BGP in the subOp. I don't understand why
this returned iterator is empty since it only executes the executor for OpBGP
and returns it.
> Purpose of EvaluatorSimple and OpExecutor
> -----------------------------------------
>
> Key: JENA-2020
> URL: https://issues.apache.org/jira/browse/JENA-2020
> Project: Apache Jena
> Issue Type: Question
> Components: ARQ
> Reporter: Martin Pekár
> Priority: Major
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> I am in the midst of adding a new operator in the transformation of OpBGP. I
> am now trying to implement the execution of the operator in the query plan,
> but I am now slightly confused about the purpose of EvaluatorSimple used in
> EvaluatorDispatch and OpExecutor. At the moment, it seems like they are doing
> the same thing. The difference seems to be that OpExecutor stores the result
> of applying the operator in a QueryIterator, whereas EvaluatorSimple stores
> its result in a Table of bindings.
> Can someone give me an explanation of purposes of these two classes and how
> they should be used?
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