Gets the session for creating asset compositions.

        return: (osid.repository.AssetCompositionDesignSession) - an
                AssetCompositionDesignSession
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_asset_composition_design() is
                false
        compliance: optional - This method must be implemented if
                    supports_asset_composition_design() is true.

def get_asset_composition_design_session(self):
        """Gets the session for creating asset compositions.

        return: (osid.repository.AssetCompositionDesignSession) - an
                AssetCompositionDesignSession
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_asset_composition_design() is
                false
        compliance: optional - This method must be implemented if
                    supports_asset_composition_design() is true.

        """
        if not self.supports_asset_composition_design():
            raise Unimplemented()
        try:
            from . import sessions
        except ImportError:
            raise OperationFailed('import error')
        try:
            session = sessions.AssetCompositionDesignSession(proxy=self._proxy,
                                                             runtime=self._runtime)
        except AttributeError:
            raise OperationFailed('attribute error')
        return session