Get identifiers for related identifiers.

def get_related_ids(self, content_id, min_strength=None):
        '''Get identifiers for related identifiers.
        '''
        related_labels = self.get_related(content_id,
                                          min_strength=min_strength)
        related_idents = set()
        for label in related_labels:
            related_idents.add(label.other(content_id))

        return list(related_idents)