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https://issues.apache.org/jira/browse/JENA-261?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13396694#comment-13396694
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Andy Seaborne commented on JENA-261:
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It's the UNION. Think of it as concatenate the results of the two arams.
The first call is no rows, the second is one row -- the concatenation is one
row.
This is a question about SPARQL Basic Federated Query spec. ARQs
implementation seems to follow the spec. If you think the spec is wrong,
you'll need to send a formal comment to the working group. I confess I don't
see why one row of no bindings was chosen other than
SERVICE silent <A> { ?m a <foo> }
SERVICE silent <B> { ?m a <foo> }
combinding the information with a join across ?m.
> QueryIterService returns an empty solution on exception
> -------------------------------------------------------
>
> Key: JENA-261
> URL: https://issues.apache.org/jira/browse/JENA-261
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ
> Affects Versions: ARQ 2.9.0, ARQ 2.9.1
> Reporter: Claude Warren
> Attachments: JENA-261_patch.txt
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> in nextStage() when a RuntimeException is caught and the 'silent' parameter
> has been set, a QueryIterSingleton is created. This results in an empty
> solution being returned. I think the proper action would be to return a
> QueryIterNullIterator so that the empty result is not returned.
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