@abc.abstractmethod<EOL><INDENT>def get_branch_id(self):<DEDENT>
return<EOL>
Gets the ``Branch Id`` representing this service branch.

        :return: the branch ``Id``
        :rtype: ``osid.id.Id``
        :raise: ``Unimplemented`` -- ``supports_journal_branching()`` is ``false``

        *compliance: mandatory -- This method must be implemented.*