def get_composition_repository_assignment_session(self):
raise Unimplemented()<EOL>
Gets the session for assigning composition to repository mappings.

        return: (osid.repository.CompositionRepositoryAssignmentSession)
                - a ``CompositionRepositoryAssignmentSession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented -
                ``supports_composition_repository_assignment()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_composition_repository_assignment()`` is ``true``.*