protected function pazpar2ShowURL($start = 0, $num = 500)
    {
        $URL = $this->getPazpar2BaseURL() . '?command=show';
        $URL .= '&query=' . urlencode($this->fullQueryString());
        $URL .= '&start=' . $start . '&num=' . $num;
        $URL .= '&sort=' . urlencode($this->sortOrderString());
        $URL .= '&block=1'; // unclear how this is advantagous but the JS client adds it
        return $URL;
    }