protected function getDocumentForUpdate($subjectOfChange, $contextAlias, Array $cbds)
    {
        foreach($cbds as $c)
        {
            if($c[_ID_KEY]==array(_ID_RESOURCE=>$this->labeller->uri_to_alias($subjectOfChange),_ID_CONTEXT=>$contextAlias))
            {
                return $c;
                break;
            }
        }

        return null;
    }