def setSubgraphVal(self,  parent_name,  graph_name, field_name, val):
subgraph = self._getSubGraph(parent_name, graph_name, True)<EOL>if subgraph.hasField(field_name):<EOL><INDENT>subgraph.setVal(field_name, val)<EOL><DEDENT>else:<EOL><INDENT>raise AttributeError("<STR_LIT>"<EOL>"<STR_LIT>" <EOL>% (field_name, graph_name, parent_name))<EOL><DEDENT>
Set Value for Field in Subgraph.

        The private method is for use in retrieveVals() method of child
        classes.

        @param parent_name: Root Graph Name
        @param graph_name:  Subgraph Name
        @param field_name:  Field Name.
        @param val:         Value for field.