protected function _convertChapterLayout(array $chapterRow) {
        $chapter = array();
        $chapter['type'] = $chapterRow['type'];
        if (!isset($chapterRow['content'])) {
            return $chapter;
        }
        $chapter['content'] = array_map(
            array($this, '_convertContentNodeLayout'),
            $chapterRow['content']
        );
        return $chapter;
    }