code: def txn_data2schema_key(self, txn: dict) -> SchemaKey:
          
  
          rv = None
          if self == Protocol.V_13:
              rv = SchemaKey(txn['identifier'], txn['data']['name'], txn['data']['version'])
          else:
              txn_txn = txn.get('txn', None) or txn  # may have already run this txn through txn2data() below
              rv = SchemaKey(
                  txn_txn['metadata']['from'],
                  txn_txn['data']['data']['name'],
                  txn_txn['data']['data']['version'])
  
          return rv
docs: Return schema key from ledger transaction data.
  
          :param txn: get-schema transaction (by sequence number)
          :return: schema key identified