使用php从xml上载中提取特定字段

I've been trying to get the id field to pull and have no idea where I'm going wrong. The rest of the data pulls correctly but I'm trying to add something new to some existing code and everything I've tried hasn't worked. Below is my XML and the PHP code I've been working off of.

I haven't worked with a combo of xml and php before so I could really use a push in the right direction.

<?xml version="1.0" encoding="UTF-8"?>
<enterprise>
   <person>
        <sourcedid>
            <source>Spirit Awards</source>
            <id>SP8675309</id>
        </sourcedid>
        <userid>...</userid>
        <name>
            <fn>...</fn>
        </name>
        <email>...</email>
    </person>

PHP code:

function get_userid(){
    return $this->uid;
}
function __construct($xmlData){
    $this->uid = (string)$xmlData->id;
}

SimpleXML^docs makes this ... well ... simple. The XML you've posted is missing a closing </enterprise> tag. Assuming the XML you're actually parsing includes the closing tag, consider:

$str = '<?xml version="1.0" encoding="UTF-8"?>
<enterprise>
   <person>
        <sourcedid>
            <source>Spirit Awards</source>
            <id>SP8675309</id>
        </sourcedid>
        <userid>...</userid>
        <name>
            <fn>...</fn>
        </name>
        <email>...</email>
    </person>
</enterprise>
';

$xml = simplexml_load_string($str);
$var = (string) $xml->person->sourcedid->id;
echo $var; // outputs: SP8675309