def get_relationship_family_session(self):
raise Unimplemented()<EOL>
Gets the ``OsidSession`` to lookup relationship/family mappings.

        return: (osid.relationship.RelationshipFamilySession) - a
                ``RelationshipFamilySession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_relationship_family()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_relationship_family()`` is ``true``.*