public boolean deleteChallenge(Challenge challenge) {
		Element challengeE;
		boolean flag = false;
		for (Iterator i = root.elementIterator("challenge"); i.hasNext();) {
			challengeE = (Element)i.next();
			if (challengeE.element("id").getText().equals(challenge.getId())) {
				challengeE.element("isDelete").setText("true");
				// Write to xml
				try {
					XmlUtils.write2Xml(fileName, document);
					return true;
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				flag = true;
				break;
			} 
		}
		return flag;
	}