Part one of Web Services Client for ILE Programming Guide (853KB) 
contains introductory material that can get you started.
From: dkimmel <dkimmel@xxxxxxxxxxxx>
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Date: 07/23/2014 09:16 AM
Subject: RE: Got a question about SOAP: can anybody recommend a
on understanding the XML?
Sent by: "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx>
To understand SOAP you need to understand XML Schema. Google XML Schema
for lots of good references.
In your example, nil="true" defines the value of the element when no value
<div>-------- Original message --------</div><div>From: "James H. H.
Lampert" <jamesl@xxxxxxxxxxxxxxxxx> </div><div>Date:07/22/2014 4:33 PM
(GMT-06:00) </div><div>To: Midrange Systems Technical Discussion
<midrange-l@xxxxxxxxxxxx> </div><div>Subject: Got a question about SOAP:
can anybody recommend a good tutorial
on understanding the XML? </div><div>
</div>Working on a project involving the use of RXS to consume a suite of
web services. SOAP web services with lots and lots of parameters (the
RXS templates for them run over 100 lines each). It's a project I've
worked on before; this time, I'm having to port the calls from one
server to another, with different server software, and (near as I can
tell) minor changes in the parameter tags (mostly capitalization changes).
It occurs to me that this would go a lot easier if I actually had an
adequate understanding of the syntax and low-level sematics of SOAP. For
example, one of the most puzzling things I see is that on the nulled-out
parameters in the RXS templates I have, it looks like each invocation of
nil is in its own namespace, e.g.,:
(the names have been changed, to protect the innocent).
I'm hoping that the more I know about SOAP, the less it's going to leave
me with a bad taste in my mouth, craving some REST.
Can somebody recommend a reference and/or tutorial that will make all
this a bit more comprehensible to me?