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Posted to dev@jena.apache.org by "Joshua Taylor (JIRA)" <ji...@apache.org> on 2014/02/03 19:14:09 UTC
[jira] [Updated] (JENA-633) subqueries with limits project more
results than they should
[ https://issues.apache.org/jira/browse/JENA-633?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Joshua Taylor updated JENA-633:
-------------------------------
Description:
A subquery with `limit 1` specified can `leak` more values to the surrounding query. Rob Vesse tracked this down to a difference between the basic algebra and the optimized algebra [1] . One query has the following basic and optimized Ops; the "join" in the former shouldn't get turned into a "sequence" in the latter.
{noformat}
Basic:
(join
(bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <urn:ex:Thing>))
(slice _ 1
(project (?resource ?p)
(order (?p)
(bgp (triple ?resource <urn:ex:p> ?p))))))
Optimized:
(sequence
(bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <urn:ex:Thing>))
(project (?resource ?p)
(top (1 ?p)
(bgp (triple ?resource <urn:ex:p> ?p)))))
{noformat}
[1] http://answers.semanticweb.com/questions/26343/outer-query-results-include-more-values-than-subquery-with-limit-n-produces/26344
was:
A subquery with `limit 1` specified can `leak` more values to the surrounding query. Rob Vesse tracked this down to a difference between the basic algebra and the optimized algebra [1] . One query has the following basic and optimized Ops; the "join" in the former shouldn't get turned into a "sequence" in the latter.
Basic:
(join
(bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <urn:ex:Thing>))
(slice _ 1
(project (?resource ?p)
(order (?p)
(bgp (triple ?resource <urn:ex:p> ?p))))))
Optimized:
(sequence
(bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <urn:ex:Thing>))
(project (?resource ?p)
(top (1 ?p)
(bgp (triple ?resource <urn:ex:p> ?p)))))
[1] http://answers.semanticweb.com/questions/26343/outer-query-results-include-more-values-than-subquery-with-limit-n-produces/26344
> subqueries with limits project more results than they should
> ------------------------------------------------------------
>
> Key: JENA-633
> URL: https://issues.apache.org/jira/browse/JENA-633
> Project: Apache Jena
> Issue Type: Bug
> Components: ARQ, Jena
> Affects Versions: Jena 2.11.0
> Reporter: Joshua Taylor
> Labels: optimization, sparql
> Attachments: SubqueryLimitBug.java
>
>
> A subquery with `limit 1` specified can `leak` more values to the surrounding query. Rob Vesse tracked this down to a difference between the basic algebra and the optimized algebra [1] . One query has the following basic and optimized Ops; the "join" in the former shouldn't get turned into a "sequence" in the latter.
> {noformat}
> Basic:
> (join
> (bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <urn:ex:Thing>))
> (slice _ 1
> (project (?resource ?p)
> (order (?p)
> (bgp (triple ?resource <urn:ex:p> ?p))))))
> Optimized:
> (sequence
> (bgp (triple ?resource <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <urn:ex:Thing>))
> (project (?resource ?p)
> (top (1 ?p)
> (bgp (triple ?resource <urn:ex:p> ?p)))))
> {noformat}
> [1] http://answers.semanticweb.com/questions/26343/outer-query-results-include-more-values-than-subquery-with-limit-n-produces/26344
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