code: package it.unibz.inf.ontop.iq.node;
  
  import com.google.common.collect.ImmutableSet;
  import it.unibz.inf.ontop.model.term.Variable;
  
  /**
   * Node that explicitly declares the variables returned by its sub-tree.
   *
   * Common abstraction for ConstructionNodes, UnionNodes, DataNodes and EmptyNodes.
   *
   */
  public interface ExplicitVariableProjectionNode extends QueryNode {
  
      /**
       * Set of variables returned by any sub-tree where this node is the root.
       */
      ImmutableSet<Variable> getVariables();
  }
  