* @throws RrdException Thrown if parsed XML template contains invalid (unrecognized) tags
*/
public RrdGraphDef getRrdGraphDef() throws RrdException {
// basic check
if (!root.getTagName().equals("rrd_graph_def")) {
throw new RrdException("XML definition must start with <rrd_graph_def>");
}
validateTagsOnlyOnce(root, new String[] {"filename", "span", "options", "datasources", "graph"});
rrdGraphDef = new RrdGraphDef();
// traverse all nodes
Node[] childNodes = getChildNodes(root);