/**
 * @author lwd
 */
var req;
function callback() {
	if (req.readyState == 4) {
		if (req.status == 200) {
			parseMessage();
		} else {
			alert("Not able to retrieve description" + req.statusText);
		}
	}
}
function parseMessage() {alert("~~~~~ 2 ajax.js~~~~~~~~");
	var xmlDoc = req.responseXML.documentElement;alert("~~~~~ 2-1 ajax.js~~~~~~~~");
	var xCous = xmlDoc.getElementsByTagName('course');
	alert("~~~~~ 3 ajax.js~~~~~~~~");
	var select_root = document.getElementById('courseName');// ???????
	alert("~~~~~ 4 ajax.js~~~~~~~~");
	select_root.options.length = 0;

	for (var i = 0; i < xCous.length; i++) {
		var xValue = xCous[i].childNodes[0].firstChild.nodeValue;
		var xText = xCous[i].childNodes[1].firstChild.nodeValue;
		try {
			select_root.options[i]=new Option(xText,xValue);
		} catch (e) {
		}
	}

}