Looking at the Amazon web services API, it's interesting to note that they provide a simpler access method than SOAP. While SOAP is a useful tool for delivering responses at a method level, it's not always appropriate for query style calls - especially where you're dealing with database data. There's just a little too much overhead there - especially if you're wanting to go straight to the display layer, rather than use the response as input to business logic.
Amazon's XML over HTTP approach is a nice balance here, as it allows you to include results direclty in web pages without needing to process information - especially as Amazon will host XSLT style sheets for you, and handle the transformations... And all you need to do is submit them the appropriate URIs in your initial HTTP query.
With regards to by interests in XML and XML application development, I'm aiming to get a bit more active on appropriate mailing lists and blogs - if I'm spending time thinking about XML in knowledge management, then I really need to share my thinking on a wider basis. It's a tack that's paying off a little, too - in a recent thread, Dave Winer agreed with me about what I consider to be the future role of RSS and RSS-like tools, as a mechanism for managing publish-and-subscribe web services.
As I wrote:
"In my XML columns for PC Plus and Application Development Advisor I've been looking at RSS as the basis for the missing half of the web services model - where we don't need dynamic generation of information, just authenticated pointers to regularly updated data.
A lot of what people are doing with web services could be more efficiently handled by using RSS or an RSS derivative as a publish and subscribe solution. RSS doesn't need to point to HTML URIs - it can point to any URI.
Once we get over the HTML hurdle, there's a whole wide world of really interesting applications out there."
What I really want to be doing right now is helping people come up with real business solutions that can be built around this model. I know that it can be done, and I have some ideas on possible scenarios - but that's not really enough.