@abc.abstractmethod<EOL><INDENT>def get_key_resource(self):<DEDENT>
return<EOL>
Gets the key resource of this entry.

        The key resource may be a student or other applicable key to
        identify a row of grading entries.

        :return: the key resource
        :rtype: ``osid.resource.Resource``
        :raise: ``OperationFailed`` -- unable to complete request

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