[jira] [Resolved] (JENA-1468) Empty VALUES clauses lose variable bindings when compiled to a SSE

["Andy Seaborne (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/JENA-1468?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andy Seaborne resolved JENA-1468.
---------------------------------
       Resolution: Fixed
         Assignee: Andy Seaborne
    Fix Version/s: Jena 3.7.0

> Empty VALUES clauses lose variable bindings when compiled to a SSE
> ------------------------------------------------------------------
>
>                 Key: JENA-1468
>                 URL: https://issues.apache.org/jira/browse/JENA-1468
>             Project: Apache Jena
>          Issue Type: Bug
>          Components: ARQ
>    Affects Versions: Jena 3.1.1, Jena 3.2.0, Jena 3.3.0, Jena 3.4.0, Jena 3.5.0, Jena 3.6.0
>            Reporter: Rick
>            Assignee: Andy Seaborne
>            Priority: Major
>              Labels: SPARQL, sse
>             Fix For: Jena 3.7.0
>
>
> Given a SPARQL query like this:
> SELECT ?foo WHERE {
>    ?foo ?bar ?baz . # Not essential for problem just to show we can't optimise it away.   
>     VALUES ?foo { }
> }
> If you compile it into an SSE with something like this:
> {{Algebra.compile(QueryFactory.create("SELECT ?foo WHERE \{ ?foo ?bar ?baz . VALUES ?foo { }}"));}}
> You end up with a semantically different SSE:
> {{(project (?foo)}}
>  {{  (join}}
>  {{    (bgp (triple ?foo ?bar ?baz))}}
>  {{    (table empty)))}} 
> Note how "(table empty)" has lost the ?foo binding, which means that this query returns all results for ?foo, where it should return no results.
> I'm not sure how this query should be expressed in SSE form I'd suggest:
> {{(table (vars ?foo) empty)}}
> Though currently this will get simplified in [code like this|https://github.com/apache/jena/blob/94eb3fc99ba1ff3991a629fffa6e6cf8b52d6c53/jena-arq/src/main/java/org/apache/jena/sparql/sse/builders/BuilderTable.java#L55-L64] into an EmptyTable if you do something like:
> {{BuilderTable.build(Item.createList((SSE.parse("(table (vars ?foo) empty)")));}}
> Additionally it appears quite a bit of code carries through this assumption that an [empty table will never have a binding|https://github.com/apache/jena/blob/94eb3fc99ba1ff3991a629fffa6e6cf8b52d6c53/jena-arq/src/main/java/org/apache/jena/sparql/algebra/table/TableEmpty.java#L57].
> As far as I can tell this issue effects many prior versions of JENA including 3.6.0.



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)