In case it didn't come through, I'm intrigued by REST, because it seems more fluid than the WS-* specifications. I can do an HTTP request in about 5 lines of socket code in any modern language, from any client device.

The WS-splat crowd seem to be building YABS (yet another brittle standard). Riddle me this: what use is a service description in a standardized form if there is only one implementor of that service? WSDL only attains full value when there are standards built on top of WSDL. Just like XML, WSDL is a meta-standard. It is a standard for specifying other standards. Collected and diverse industry behemoths and leviathans make the rules for that playground.

I see two, equally likely, outcomes for any given service definition:

Once such interfaces are defined, how easily might they be changes? I mean the WSDL (or other) definition of the service itself. Can anyone say CORBAservices? You'd better define your services right the first time, because there appears to be substantial friction opposing change.

How does REST avoid this issue? By eliminating layers. If I support a URI naming scheme like as a RESTful way to access purchase orders, and I find that we need to change it to /purchaseOrders/departmentNumber/poNumber, then both forms can co-exist. The alternative change in SOAP/WSDL-land would either modify the original endpoint (an incompatible change!) or would define a new service to support the new mode of lookup. (I suppose other hacks are available, too. Service.getPurchaseOrder2() or Service.getPurchaseOrderNew() for example.)

Of course, neither of these service architectures are implemented widely enough to really evaluate which one will be more accepting of change. I can tell you, though, that one of the huge CORBA-killers was the slow pace and resistance to change in the CORBAservices.