XML to PHP

Ciao Everyone,
I’m using this code here to import text to a web page from an xml file.

My problem is that at the beginning of the code it links to the file $file = "data.xml";
It works if I use a normal file as the example but what i want it to do is to link to my channel dejandj.net/?feed=podcast
How do i do this?Because if I just substitute the “data.xml” with the url of the channel it doesn’t work.

Thank you very much for your help