I got a chance to talk to Arthur Ryman last month, for a few minutes, so took full advantage of the situation and launched into a rant/whine on WSDL. I gave him a brief synopsis of what we're trying to do on the project I'm working on (can't talk about it right now, sorry), and he made an interesting statement. "You're trying to use Web Services to do Distributed Objects. You should think in terms of document exchange instead." Not an exact quote, but pretty close.
I've been thinking about that a lot lately.
He's right, and he's wrong. We are/were trying to do distributed objects, and I really should know better than to even think about this. I've done CORBA ORB implementations, and worked on IBM's VisualAge Distributed Smalltalk project. Been there, done that, know it's a freaking mess. Even when you get it technically working, it becomes difficult to disentangle your object mess with your distribution mess. I've never seen it work well. So, he's right in that we shouldn't be doing distributed objects.
Where I think he's wrong is that we have to think in terms of documents. If you're doing nothing but storing documents, I guess it's fine. But really, we got clients wanting to talk to servers and presumably they want to send data back. Not documents. Then I have to map a document to data and back. Ick. Especially when the 'spec' way to do this is with the unbelievably horrible xsi spec (sorry Dave, I'm not smart enough for this stuff, or maybe I'm too old).
That's why JSON intrigues me. Data. Yummy, yummy, data. And really, I think you could take a view of Web Services using XML as a problem looking for a solution. There are few languages where mucking with DOMs is in any sense fun. I even had a chance to play with REXML last night, and, while I can write some pretty compact code to do interesting stuff, I still need to understand either DOM or XPath to do it. XPATH is another one of those things that's almost too hard. I can remember the easy bits, but then always need to go back to the inscrutable spec to get my work done. Ick.
Another interesing use case for the JSON stuff is returning arbitrary SQL result sets over the wire. If you want to XML-ize this, in such a way that you can easily WSDL it up, and have programming language bindings that are at all usable, you end up with a story where you have something like an SDO that wraps all your objects. And then the XML looks like crap, and just adds more overhead. The answer: remove the strict typing requirement!