Class TransformFilterInequality

  • All Implemented Interfaces:
    Transform

    public class TransformFilterInequality
    extends TransformCopy
    A transform that aims to optimize queries where there is an inequality constraint on a variable in an attempt to speed up evaluation e.g
     PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
     SELECT *
     WHERE
     {
       ?s rdf:type <http://type> ;
          ?p ?o .
       FILTER(?p != rdf:type)
     }
     
    Would transform to the following:
     PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
     SELECT *
     WHERE
     {
       ?s rdf:type <http://type> ;
          ?p ?o .
       MINUS { VALUES ?p { rdf:type } }
     }
     

    Status

    Performance testing has shown that often this gives minimal performance benefit so this optimization is not enabled by default. It may be explicitly enabled by setting the ARQ.optFilterInequality symbol in your Context or the ARQ global context (ARQ.getContext() to true

    Applicability

    This optimizer is conservative in that it only makes the optimization where the inequality constraint is against a non-literal as otherwise substituting the value changes the query semantics because it switches from value equality to the more restrictive term equality. The optimization is safe for non-literals because for those value and term equality are equivalent (in fact value equality is defined to be term equality).

    There are also various nested algebra structures that can make the optimization unsafe and so it does not take place if any of those situations is detected.

    • Constructor Detail

      • TransformFilterInequality

        public TransformFilterInequality()
        Creates a new transform