private String dataFunction(String expresion) {
        int i = expresion.indexOf("(");
        int j = expresion.length() - 1;

        if (expresion.charAt(j) != ')') {
            j = -1;
        }

        if (i < 0 || j == -1) {
            return null;
        }

        String data = expresion.substring(i + 1, j);
        if (!okParentesis(data)) {
            return null;
        }

        String name = expresion.substring(0, i);

        for (int k = 0; k < name.length(); k++) {
            if (NOCARAC.indexOf(expresion.substring(k, k + 1)) >= 0) {
                return null;
            }
        }

        return name.trim() + ";" + data;
    }