@abc.abstractmethod<EOL><INDENT>def get_families_by_provider(self, resource_id):<DEDENT>
return<EOL>
Gets a ``FamilyList`` from the given provider.

        In plenary mode, the returned list contains all known families
        or an error results. Otherwise, the returned list may contain
        only those families that are accessible through this session.

        :param resource_id: a resource ``Id``
        :type resource_id: ``osid.id.Id``
        :return: the returned ``Family list``
        :rtype: ``osid.relationship.FamilyList``
        :raise: ``NullArgument`` -- ``resource_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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