Dictionary of all datastreams that belong to this object in Fedora.
        Key is datastream id, value is an :class:`ObjectDatastream` for that
        datastream.

        Only retrieved when requested; cached after first retrieval.

def ds_list(self):      # NOTE: how to name to distinguish from locally configured datastream objects?
        """
        Dictionary of all datastreams that belong to this object in Fedora.
        Key is datastream id, value is an :class:`ObjectDatastream` for that
        datastream.

        Only retrieved when requested; cached after first retrieval.
        """
        # FIXME: how to make access to a versioned ds_list ?

        if self._ds_list is None:
            self._ds_list = self._get_datastreams()
        return self._ds_list