def get_tid2annotations(self, clean:bool=True):
        ''' clean: for list of literals only '''
        tid2annotations = defaultdict(list)
        header = ['Index'] + list(self.fetch_annotations().columns)
        for row in self.fetch_annotations().itertuples():
            row = {header[i]:val for i, val in enumerate(row)}
            if clean:
                annotation = {
                    'tid': row['tid'],
                    'annotation_type_tid': row['annotation_type_tid'],
                    'value': row['value'],
                    'annotation_type_label': row['annotation_type_label'],
                }
                tid2annotations[row['tid']].append(annotation)
            elif not clean:
                tid2annotations[row['tid']].append(row)
        return tid2annotations