if (_fieldDesc == null) {
// read the URL to get the query arguments
try {
URL url =_makeURL(_url, "FORMAT=METADATA");
LOG.info("Reading SLAP server configuration from " + _url);
VOElement topEl = new VOElementFactory(StoragePolicy.getDefaultPolicy())
.makeVOElement(new URLDataSource(url));
_checkStatus(topEl);
NodeList params = topEl.getElementsByTagName("PARAM");
_fieldDesc = new FieldDescAdapter[params.getLength()];