RPG消耗的PHP SOAP Web服务是否需要WSDL？

I have a very basic, beginners PHP web service:

<?php

function EchoText($text){
    return "ECHO: ".$text;
}

$server = new SoapServer(null,
                         array('uri' => "urn://tyler/res"));
$server->addFunction('EchoText');
$server->handle();

?>

I understand some basics about WSDL's... that they "explain" how to access a web service, what functions it has, what parameters that function contains, and what the return value could be.

Question 1) do I need to create a WSDL for an RPG program which will call my web service?

Question 2) if yes to #1 -> do I need to manually do this by creating a new .xml document?

Question 3) if yes to #2 -> could someone provide me a sample WSDL for such a simple web service (my example above)? I could then build my code and expand off the example.

Thanks in advance for any help, suggestions or links!