Returns parent aliases for a list of child IDs.

        :param list child_ids:
        :rtype: set
        :return: a set of parent aliases

def get_parents_for(self, child_ids):
        """Returns parent aliases for a list of child IDs.

        :param list child_ids:
        :rtype: set
        :return: a set of parent aliases
        """
        self._cache_init()
        parent_candidates = []
        for parent, children in self._cache_get_entry(self.CACHE_NAME_PARENTS).items():
            if set(children).intersection(child_ids):
                parent_candidates.append(parent)
        return set(parent_candidates)