AbstractLogicalOperator producerOp = (AbstractLogicalOperator) op.getInputs().get(0).getValue();
switch (producerOp.getOperatorTag()) {
case EMPTYTUPLESOURCE:
return new HashMap<Integer, DocumentOrder>();
case NESTEDTUPLESOURCE:
NestedTupleSourceOperator nestedTuplesource = (NestedTupleSourceOperator) producerOp;
return getProducerDocumentOrderVariableMap(nestedTuplesource.getDataSourceReference().getValue(),
vxqueryContext);
default:
return new HashMap<Integer, DocumentOrder>(
vxqueryContext.getDocumentOrderOperatorVariableMap(producerOp));
}