code: def _load_data(self,
                     equities,
                     futures,
                     exchanges,
                     root_symbols,
                     equity_supplementary_mappings):
          
          # Set named identifier columns as indices, if provided.
          _normalize_index_columns_in_place(
              equities=equities,
              equity_supplementary_mappings=equity_supplementary_mappings,
              futures=futures,
              exchanges=exchanges,
              root_symbols=root_symbols,
          )
  
          futures_output = self._normalize_futures(futures)
  
          equity_supplementary_mappings_output = (
              self._normalize_equity_supplementary_mappings(
                  equity_supplementary_mappings,
              )
          )
  
          exchanges_output = _generate_output_dataframe(
              data_subset=exchanges,
              defaults=_exchanges_defaults,
          )
  
          equities_output, equities_mappings = self._normalize_equities(
              equities,
              exchanges_output,
          )
  
          root_symbols_output = _generate_output_dataframe(
              data_subset=root_symbols,
              defaults=_root_symbols_defaults,
          )
  
          return AssetData(
              equities=equities_output,
              equities_mappings=equities_mappings,
              futures=futures_output,
              exchanges=exchanges_output,
              root_symbols=root_symbols_output,
              equity_supplementary_mappings=equity_supplementary_mappings_output,
          )
docs: Returns a standard set of pandas.DataFrames:
          equities, futures, exchanges, root_symbols