把从SQL中取出的数据转化成XMl格式

    */
    function XML_sql2xml ($dsn = Null, $root = "root") {

        // if it's a string, then it must be a dsn-identifier;

        if (is_string($dsn))
        {
            include_once ("DB.php");
            $this->db = DB::Connect($dsn);
            if (DB::isError($this->db))
            {
                print "The given dsn for XML_sql2xml was not valid in file ".__FILE__." at line ".__LINE__."<br>n";
                return new DB_Error($this->db->code,PEAR_ERROR_DIE);
            }

        }

        elseif (is_object($dsn) && DB::isError($dsn))
        {
            print "The given param for XML_sql2xml was not valid in file ".__FILE__." at line ".__LINE__."<br>n";
            return new DB_Error($dsn->code,PEAR_ERROR_DIE);
        }

        // if parent class is db_common, then it's already a connected identifier
        elseif (get_parent_class($dsn) == "db_common")
        {
            $this->db = $dsn;
        }

        $this->xmldoc = domxml_new_xmldoc('1.0');

        //oehm, seems not to work, unfortunately.... does anybody know a solution?
        $this->xmldoc->encoding = $this->encoding_to;        

        if ($root) {
            $this->xmlroot = $this->xmldoc->add_root($root);
            //PHP 4.0.6 had $root->name as tagname, check for that here...
            if (!isset($this->xmlroot->{$this->tagname}))
            {