Array length from database generated xml

New here.

I want to know the length of a xml. From a xml file I can make it work.

In this case it’s a database that generates the xml. So it is a URL, not a Xml.

How can I make this work?

// loading xml //

url_xml.onLoad = function() {
    // this is the array I need from the URL // 	
    var array1:Array = url_xml; 

    //In a xml file case, I could add ".childnodes;". I tried here and the output wasn't right. 

    trace (array1.length); // output

url_xml.load("http://.../contents/?format=xml"); // xml path generated from database//

Any ideas? thanks!!