Return the list of attributes associated with the specified relation.
        :param name: A name of a relation in the Schema.
        :return: A list of attributes.
        :raise RelationReferenceError: Raised if the name does not exist.

def get_attributes(self, name):
        """
        Return the list of attributes associated with the specified relation.
        :param name: A name of a relation in the Schema.
        :return: A list of attributes.
        :raise RelationReferenceError: Raised if the name does not exist.
        """
        attributes = self._data.get(name, None)
        if not attributes:
            raise RelationReferenceError(
                'Relation \'{name}\' does not exist.'.format(name=name))
        return attributes[:]