code: def getSubgraphFieldList(self, parent_name, graph_name):
          
          graph = self._getSubGraph(parent_name, graph_name, True)
          return graph.getFieldList()
docs: 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.