public void SaveXML(File file) {
        tableName = operand.getTableName();

        try {

            DocumentBuilderFactory docFactory = DocumentBuilderFactory
                    .newInstance();
            DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
            // root elements
            Document doc = docBuilder.newDocument();
            // System.out.println("saving "+tableName);
            rootElement = doc.createElement(tableName);
            for (int cnt = 0; cnt < operand.getAttributes().size(); cnt++) {
                rootElement.setAttribute(operand.getAttributes().get(cnt),
                        operand.getColumn(operand.getAttributes().get(cnt)).get(0)
                                .getClass().getName());
            }
            rootElement.setAttribute("attrNum", Integer.toString(operand
                    .getAttributes().size()));

            doc.appendChild(rootElement);

            for (int i = 0; i < operand.getColumn(operand.getAttributes().get(
                    0)).size(); i++) {
                // className elements

                Element element = doc.createElement("row");
                rootElement.appendChild(element);

                for (int j = 0; j < operand.getAttributes().size(); j++) {
                    String s = operand.getColumn(operand.getAttributes().get(j))
                            .get(i).toString();
                    Element className = doc.createElement(operand
                            .getAttributes().get(j));
                    className.appendChild(doc.createTextNode(s));
                    element.appendChild(className);
                }

            }
            // write the content into xml file
            TransformerFactory transformerFactory = TransformerFactory
                    .newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMImplementation domImpl = doc.getImplementation();
            DocumentType doctype = domImpl.createDocumentType("doctype", "",
                    tableName + ".dtd");
            transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, doctype
                    .getSystemId());
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(file);

            transformer.transform(source, result);

        } catch (ParserConfigurationException pce) {

        } catch (TransformerException tfe) {

        }

    }