def IsDefault(self):
    """Determines if the data stream is the default data stream.

    Returns:
      bool: True if the data stream is the default data stream, false if not.
    """
    if not self._tsk_attribute or not self._file_system:
      return True

    if self._file_system.IsHFS():
      attribute_type = getattr(self._tsk_attribute.info, 'type', None)
      return attribute_type in (
          pytsk3.TSK_FS_ATTR_TYPE_HFS_DEFAULT, pytsk3.TSK_FS_ATTR_TYPE_HFS_DATA)

    if self._file_system.IsNTFS():
      return not bool(self.name)

    return True