Package org.eclipse.rdf4j.federated.util

Class QueryAlgebraUtil

java.lang.Object
org.eclipse.rdf4j.federated.util.QueryAlgebraUtil
public class QueryAlgebraUtil extends Object
Various static functions for query handling and parsing (alegbra expression).
Author:
Andreas Schwarte

  • Constructor Details

    • QueryAlgebraUtil

      public QueryAlgebraUtil()

  • Method Details

    • hasFreeVars

      public static boolean hasFreeVars(StatementPattern stmt, BindingSet bindings)
      returns true iff there is at least one free variable, i.e. there is no binding for any variable
      Parameters:
      stmt -
      bindings -
      Returns:
      whether there is at least one free variable

    • getVarValue

      public static Value getVarValue(Var var, BindingSet bindings)
      Return the Value of the variable which is either taken from the variable itself (bound) or from the bindingsset (unbound).
      Parameters:
      var -
      bindings - the bindings, must not be null, use EmptyBindingSet instead
      Returns:
      the value or null

    • toTupleExpr

      public static TupleExpr toTupleExpr(ArbitraryLengthPath node, Set<String> varNames, BindingSet bindings)
      Convert the given ArbitraryLengthPath to a fresh TupleExpr where all provided bindings are bound.
      Parameters:
      node -
      varNames -
      bindings -
      Returns:
      the fresh and bound expression

    • toStatementPattern

      public static StatementPattern toStatementPattern(Statement stmt)

    • toStatementPattern

      public static StatementPattern toStatementPattern(Resource subj, IRI pred, Value obj)

    • toStatement

      public static Statement toStatement(StatementPattern stmt)

    • toStatement

      public static Statement toStatement(StatementPattern stmt, BindingSet bindings)

    • selectQuery

      public static TupleExpr selectQuery(StatementPattern stmt, BindingSet bindings, FilterValueExpr filterExpr, AtomicBoolean evaluated) throws IllegalQueryException
      Construct a SELECT query for the provided statement.
      Parameters:
      stmt -
      bindings -
      filterExpr -
      evaluated - parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning
      Returns:
      the SELECT query
      Throws:
      IllegalQueryException

    • selectQuery

      public static TupleExpr selectQuery(ExclusiveGroup group, BindingSet bindings, FilterValueExpr filterExpr, AtomicBoolean evaluated)
      Construct a SELECT query for the provided ExclusiveGroup. Note that bindings and filterExpr are applied whenever possible.
      Parameters:
      group - the expression for the query
      bindings - the bindings to be applied
      filterExpr - a filter expression or null
      evaluated - parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning
      Returns:
      the SELECT query

    • selectQueryBoundUnion

      public static TupleExpr selectQueryBoundUnion(StatementPattern stmt, List<BindingSet> unionBindings, FilterValueExpr filterExpr, Boolean evaluated)
      Construct a SELECT query expression for a bound union.

      Pattern:

      SELECT ?v_1 ?v_2 ?v_N WHERE { { ?v_1 p o } UNION { ?v_2 p o } UNION ... }

      Note that the filterExpr is not evaluated at the moment.

      Parameters:
      stmt -
      unionBindings -
      filterExpr -
      evaluated - parameter can be used outside this method to check whether FILTER has been evaluated, false in beginning
      Returns:
      the SELECT query

    • selectQueryStringBoundCheck

      public static TupleExpr selectQueryStringBoundCheck(StatementPattern stmt, List<BindingSet> unionBindings)
      Construct a SELECT query for a grouped bound check.

      Pattern:

      SELECT DISTINCT ?o_1 .. ?o_N WHERE { { s1 p1 ?o_1 FILTER ?o_1=o1 } UNION ... UNION { sN pN ?o_N FILTER ?o_N=oN }}

      Parameters:
      stmt -
      unionBindings -
      Returns:
      the SELECT query

    • constructInnerUnion

      protected static Union constructInnerUnion(StatementPattern stmt, int outerID, Set<String> varNames, List<BindingSet> bindings)

    • constructStatement

      protected static StatementPattern constructStatement(StatementPattern stmt, Set<String> varNames, BindingSet bindings)
      Construct the statement string, i.e. "s p o . " with bindings inserted wherever possible. Note that the free variables are added to the varNames set for further evaluation.
      Parameters:
      stmt -
      varNames -
      bindings -
      Returns:
      the StatementPattern

    • constructStatementId

      protected static StatementPattern constructStatementId(StatementPattern stmt, String varID, Set<String> varNames, BindingSet bindings)
      Construct the statement string, i.e. "s p o . " with bindings inserted wherever possible. Variables are renamed to "var_"+varId to identify query results in bound queries. Note that the free variables are also added to the varNames set for further evaluation.
      Parameters:
      stmt -
      varNames -
      bindings -
      Returns:
      the StatementPattern

    • constructStatementCheckId

      protected static TupleExpr constructStatementCheckId(StatementPattern stmt, int varID, Set<String> varNames, BindingSet bindings)
      Construct the statement string, i.e. "s p ?o_varID FILTER ?o_N=o ". This kind of statement pattern is necessary to later on identify available results.
      Parameters:
      stmt -
      varID -
      varNames -
      bindings -
      Returns:
      the expression

    • appendVar

      protected static Var appendVar(Var var, Set<String> varNames, BindingSet bindings)
      Clone the specified variable and attach bindings.
      Parameters:
      var -
      varNames -
      bindings -
      Returns:
      the variable

    • appendVarId

      protected static Var appendVarId(Var var, String varID, Set<String> varNames, BindingSet bindings)
      Clone the specified variable and attach bindings, moreover change name of variable by appending "_varId" to it.
      Parameters:
      var -
      varID -
      varNames -
      bindings -
      Returns:
      the variable

    • getFreeVars

      public static Collection<String> getFreeVars(TupleExpr tupleExpr)
      Computes the collection of free variables in the given TupleExpr.
      Parameters:
      tupleExpr - the expression
      Returns:
      the free variables
      See Also: