public static void importDefaultUnits() {
            SAXBuilder sxb = new SAXBuilder();
            
            try 
            {
                Document fic = sxb.build(new File("units.xml"));
                Element root = fic.getRootElement();
                
                List<Element> systems = root.getChild("systems").getChildren("system");
                for (int i = 0; i < systems.size();i++) {
                    addSystem(systems.get(i).getAttributeValue("name"));
                }
                
                List<Element> types = root.getChild("types").getChildren("type");
                for (int i = 0; i < types.size(); i++) {
                    addType(types.get(i).getAttributeValue("name"));
                }

                List<Element> units = root.getChild("units").getChildren("unit");
                for (int i = 0; i < units.size(); i++) {
                    Element unit = units.get(i);
                    String name = unit.getAttributeValue("mètre");
                    String systemName = unit.getAttributeValue("system");
                    String typeName = unit.getAttributeValue("type");
                    
                    if(unit.getChildTextTrim("reference-unit").equalsIgnoreCase("true")) {
                        // si l'unité est une unité de référence
                        addReferenceUnit(name, typeName, systemName);
                    } else {
                        // si 'unité n'est pas une unité de référence
                        String strFactor = unit.getChildTextTrim("factor-to-reference");
                        double factor = Double.parseDouble(strFactor);
                        
                        if(unit.getChild("factor-to-reference").getAttributeValue("division").equalsIgnoreCase("yes")) {
                            factor = 1 / factor;
                        }
                        
                        addStandardUnit(name, typeName, systemName, factor);
                    }
                }
                
            } catch (Exception e) {}
        }