the ids of the data nodes that are used by the specified procedure node.
Returns NULL if there is no node with the given id, the id is not for
a procedure node, or the procedure node does not use any data nodes. The last case
can occur, for example, if the procedure node represents a statement where
a constant is assigned to a variable.
the ids of the data nodes that are created by the specified procedure node.
Returns NULL if there is no node with the given id, the id is not for
a procedure node, or the procedure node does not create any data nodes. The last case
can occur, for example, if the procedure node represents a statement where
the statement prints a constant string.
the ids of the data nodes that are updated by the specified procedure node.
Returns NULL if there is no node with the given id, the id is not for
a procedure node, or the procedure node does not update any data.