def assign_relationship_to_family(self, relationship_id=None, family_id=None):
pass<EOL>
Adds an existing ``Relationship`` to a ``Family``.

        arg:    relationship_id (osid.id.Id): the ``Id`` of the
                ``Relationship``
        arg:    family_id (osid.id.Id): the ``Id`` of the ``Family``
        raise:  AlreadyExists - ``relationship_id`` is already assigned
                to ``family_id``
        raise:  NotFound - ``relationship_id`` or ``family_id`` not
                found
        raise:  NullArgument - ``relationship_id`` or ``family_id`` is
                ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        *compliance: mandatory -- This method must be implemented.*