public function getComment()
    {
        $returnValue = (string) '';
        if($this->comment == '') {
            $comment =  $this->getOnePropertyValue($this->getProperty(OntologyRdfs::RDFS_COMMENT));
            $this->comment = $comment != null ? $comment->literal : '';
             
        }
        $returnValue = $this->comment;
        return (string) $returnValue;
    }