10. The method of claim 9 , wherein the plan includes an operator for deriving a value associated with a node of the markup language document.
10. The method of claim 9 , wherein the plan includes an operator for deriving a value associated with a node of the markup language document. 11. The method of claim 10 , wherein said determining step includes placing an operator for deriving a value below the operator representing the function in the plan so as to input derived values into the function.