function to_tripod_array($docId,$context)
    {
        $docId = $this->_labeller->qname_to_alias($docId);
        $contextAlias = $this->_labeller->uri_to_alias($context);

        if ($docId!=null)
        {
            $subjects = $this->get_subjects();
            foreach ($subjects as $subject)
            {
                if ($subject==$docId)
                {
                    $graph = $this->get_subject_subgraph($subject);
                    $doc = $this->index_to_tarray($graph,$contextAlias);
                    return $doc;
                }
            }
        }
        return null;
    }