'Returns a standard set of pandas.DataFrames:
equities, futures, exchanges, root_symbols'

def _load_data(self, equities, futures, exchanges, root_symbols, equity_supplementary_mappings):

    for (df, id_col) in [(equities, 'sid'), (futures, 'sid'), (exchanges, 'exchange'), (root_symbols, 'root_symbol')]:
        if (id_col in df.columns):
            df.set_index(id_col, inplace=True)
    (equities_output, equities_mappings) = self._normalize_equities(equities)
    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)
    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)
