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https://issues.apache.org/jira/browse/JENA-2020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17255226#comment-17255226
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Andy Seaborne commented on JENA-2020:
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Only one per execution - which is determined by {{QueryEngineFactory}} and
{{QueryEngineRegistry}}.
Not sure what you mean by "before" here. The {{QueryIterator}} passed into an
evaluation step is the previous stage if it is part of an {{OpSequence}} or
{{OpDisjunction}} otherwise it is step below in the execution tree (see, for
example, {{OpJoin}}).
> 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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