def getSubgraphFieldList(self, parent_name, graph_name):
graph = self._getSubGraph(parent_name, graph_name, True)<EOL>return graph.getFieldList()<EOL>
Returns list of names of fields for subgraph with name graph_name
        and parent graph with name parent_name.

        @param parent_name: Root Graph Name
        @param graph_name:  Subgraph Name
        @return:            List of field names for subgraph.