code: def update_relationship(self, relationship_form):
          
          # Implemented from template for
          # osid.resource.ResourceAdminSession.update_resource_template
          collection = JSONClientValidated('relationship',
                                           collection='Relationship',
                                           runtime=self._runtime)
          if not isinstance(relationship_form, ABCRelationshipForm):
              raise errors.InvalidArgument('argument type is not an RelationshipForm')
          if not relationship_form.is_for_update():
              raise errors.InvalidArgument('the RelationshipForm is for update only, not create')
          try:
              if self._forms[relationship_form.get_id().get_identifier()] == UPDATED:
                  raise errors.IllegalState('relationship_form already used in an update transaction')
          except KeyError:
              raise errors.Unsupported('relationship_form did not originate from this session')
          if not relationship_form.is_valid():
              raise errors.InvalidArgument('one or more of the form elements is invalid')
          collection.save(relationship_form._my_map)
  
          self._forms[relationship_form.get_id().get_identifier()] = UPDATED
  
          # Note: this is out of spec. The OSIDs don't require an object to be returned:
          return objects.Relationship(
              osid_object_map=relationship_form._my_map,
              runtime=self._runtime,
              proxy=self._proxy)
docs: Updates an existing relationship.
  
          arg:    relationship_form (osid.relationship.RelationshipForm):
                  the form containing the elements to be updated
          raise:  IllegalState - ``relationship_form`` already used in an
                  update transaction
          raise:  InvalidArgument - the form contains an invalid value
          raise:  NullArgument - ``relationship_form`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          raise:  Unsupported - ``relationship_form`` did not originate
                  from ``get_relationship_form_for_update()``
          *compliance: mandatory -- This method must be implemented.*