def entities(self, subject_id):
        """ Returns all the entities of assertions for a subject, disregarding
        whether the assertion still is valid or not.

        :param subject_id: The identifier of the subject
        :return: A possibly empty list of entity identifiers
        """
        res = self._cache.get(subject_id)
        if not res:
            raise KeyError("No such subject")
        else:
            return res