@abc.abstractmethod<EOL><INDENT>def get_obsolete_installations(self):<DEDENT>
return<EOL>
Gets the installations whose packages are obsolete.

        :return: the obsolete installations
        :rtype: ``osid.installation.InstallationList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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