[JENA-1534] Variables in EXISTS must be considered for the join strategy

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Jena 3.7.0
• Fix Version/s: Jena 3.8.0
• Component/s: ARQ
• Assignee: Andy Seaborne
• Reporter: Andy Seaborne
• Created: 27/Apr/18 18:03
• Updated: 29/Jun/18 10:13
• Resolved: 29/Apr/18 15:10

Description

This query has a join between the GRAPH and the pattern before it.

SELECT  *
WHERE
  { ?s  ?p  ?V0
    GRAPH ?g 
      { ?sx  ?p  ?ox
        FILTER EXISTS { _:b0  ?p  ?V0 }
      }
  }

The fact ?V0 occurs in the LHS of the join in ?s ?p ?V0 and in the FILTER but not in the rest of the RHS means the "sequence" transform can not be used.

Contrast to:

SELECT  *
WHERE
  { ?s  ?p  ?V1
    GRAPH ?g 
      { ?sx  ?p  ?ox
        FILTER EXISTS { _:b0  ?p  ?V2 }
      }
  }

Now ?V2 is only in the FILTER so it is safe to transform the join.

Note that ?p appears in LHS so making it defined in the EXISTS and the sequence transfrom is possible.

Issue Links

• relates to: JENA-1167 Variables used in a filter and then defined are not handled properly by the join strategy.
• relates to: JENA-1280 JoinClassifer is too cautious with EXISTS variables.
• links to: GitHub Pull Request #409