PHP SOAP服务器返回没有标记的XML

我有以下php服务器代码:

$xml ="<?xml version='"1.0'" encoding='"UTF-8'"?>";
$root = "Data";
$warmdata = "WarmData";
$brinedata = "BrineData";
$permindata = "PerMinData";
$xml .= "<$root>";
    $xml .= "<$warmdata>";
        foreach($result as $row)
        {
            $xml .= "<WarmIn>";
            $xml .= $row['value'] . " " . $row['time'];
            $xml .= "</WarmIn>";
        }
        foreach($result2 as $row)
        {
            $xml .= "<WarmOut>";
            $xml .= $row['value'] . " " . $row['time'];
            $xml .= "</WarmOut>";
        }
    $xml .= "</$warmdata>";
    $xml .= "<$brinedata>";
        foreach($result3 as $row)
        {
            $xml .= "<BrineIn>";
            $xml .= $row['value'] . " " . $row['time'];
            $xml .= "</BrineIn>";
        }
        foreach($result4 as $row)
        {
            $xml .= "<BrineOut>";
            $xml .= $row['value'] . " " . $row['time'];
            $xml .= "</BrineOut>";
        }
    $xml .= "</$brinedata>";
    $xml .= "<$permindata>";
        foreach($result5 as $row)
        {
            $xml .= "<WarmPerMin>";
            $xml .= $row['value'] . " " . $row['time'];
            $xml .= "</WarmPerMin>";
        }
        foreach($result6 as $row)
        {
            $xml .= "<BrinePerMin>";
            $xml .= $row['value'] . " " . $row['time'];
            $xml .= "</BrinePerMin>";
        }
    $xml .= "</$permindata>";
$xml .= "</$root>";
header ("Content-Type:text/xml");
return $xml;
$options=array('uri'=>'http://localhost/');
$server = new SoapServer(NULL,$options);
$server->setClass('DBData');
$server->handle();

我正在尝试使用soap客户机获得格式正确的xml输出，但是当我请求xml时，输出仅包含从数据库中检索到的单行数字，而没有实际的xml标记。我如何修改它，以便在输出中有标签?