@abc.abstractmethod<EOL><INDENT>def get_relationships(self):<DEDENT>
return<EOL>
Gets all ``Relationships``.

        :return: a list of ``Relationships``
        :rtype: ``osid.relationship.RelationshipList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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