Package se.liu.ida.hefquin.engine

Class ValuesServiceQueryResolver

java.lang.Object
se.liu.ida.hefquin.engine.ValuesServiceQueryResolver
public class ValuesServiceQueryResolver extends Object
Queries with a WHERE clause of a form such as the following one need to be rewritten, which is what this class does. 
 PREFIX ex: <http://example.org/>

 SELECT * WHERE {
   VALUES (?s1 ?s2) {
     (ex:endpoint1 ex:endpoint2)
     (ex:endpoint1 ex:endpoint3)
   }
   SERVICE ?s1 { .. some pattern (that neither mention ?s1 nor ?2) .. }
   SERVICE ?s2 { .. also some pattern (that also doesn't mention ?s1 or ?2) .. }
 }
The rewriting that is applied to such query patterns is to apply the solution mappings of the VALUES clause to the SERVICE clauses and, then remove the VALUES clause. If the VALUES clause contains multiple solution mappings (as in the example above), than the group of SERVICE clauses is copied for each of these solution mappings, and the resulting groups are combined via UNION. For instance, the result of rewriting the example query above is given as follows. 
 PREFIX ex: <http://example.org/>

 SELECT * WHERE {
   {
     SERVICE ex:endpoint1 { .. some pattern (that neither mention ?s1 nor ?2) .. }
     SERVICE ex:endpoint2 { .. also some pattern (that also doesn't mention ?s1 or ?2) .. }
   }
   UNION
   {
     SERVICE ex:endpoint1 { .. some pattern (that neither mention ?s1 nor ?2) .. }
     SERVICE ex:endpoint3 { .. also some pattern (that also doesn't mention ?s1 or ?2) .. }
   }
 }

  • Constructor Details

    • ValuesServiceQueryResolver

      public ValuesServiceQueryResolver()

  • Method Details

    • expandValuesPlusServicePattern

      public static void expandValuesPlusServicePattern(org.apache.jena.query.Query q)
      If the WHERE clause of the given query is of a form that should be rewritten (as is checked by using isQueryToBeExpanded(Query)), then this method replaces the WHERE clause of the query by the rewritten one. Otherwise, the WHERE clause of the query is not changed.

    • isQueryToBeExpanded

      public static boolean isQueryToBeExpanded(org.apache.jena.query.Query q)
      Returns true if the WHERE clause of the given query is of a form that should be rewritten. That is, the WHERE clause must begin with a VALUES clause, none of the variables bound by the VALUES clause is mentioned anywhere else except as the variable of a SERVICE clause, the VALUES clause must mention every variable that is a variable of a SERVICE clause, there must be at least one SERVICE clause with a variable, and there must not be any other VALUES clause in the WHERE clause.

    • rewrite

      protected static org.apache.jena.sparql.syntax.Element rewrite(org.apache.jena.sparql.syntax.ElementGroup eg, org.apache.jena.sparql.engine.binding.Binding solmap)

    • rewrite

      protected static org.apache.jena.sparql.syntax.Element rewrite(Iterator<org.apache.jena.sparql.syntax.Element> it, org.apache.jena.sparql.engine.binding.Binding solmap)