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"Consider that WSDL allows one to specify bindings for HTTP GET. Any XML/SOAP web service with this binding can be called via a URI with all the benefits of REST Paul outlines."
Okay, but if you're using HTTP and WSDL, then you aren't using SOAP. So it isn't a subset, it's an alternative. Unfortunately, WSDL is a fairly poor interface definition language for web services built using a web architecture. The problem is that a WSDL defines *exactly one Web resource*. It's like having a very precise definition for one page of XML.com and the rest is undefined. As soon as you follow a hyperlink to another web resource, you have lost any of the static type checking features provided by WSDL. If you try to build a real application this way you will find that WSDL is next to useless.
By the way, insofar as SOAP is designed to allow you to send messages to a SINGLE web resource end-point, you could actually think of it as limited compared to REST.
"What REST seem to be missing is a means for self-description."
There are a couple of projects working on that. My personal project is called WRDL and you can find it on www.prescod.net. Mark Baker is working on something based on RDF.
"How do I as a client know what URI's are supported?"
I would rephrase this as:
* what XML document types and other media types are supported as inputs and outputs
* what operations are available on them.
People tend to over-emphasize URIs. URIs are the most critical technology, yes, but you don't go around building services by handing people lists of URIs. Rather you hand them a SINGLE URI and that resource will typically be represented by an XML document that can refer to other resources and so forth.
"On the REST-ful client end I'm back to thumbing through (hopefully) up-to-date API documentation to get the syntax of each call."
REST is just as amenable to static description as RPC is. The REST static description languages under development are much simpler, easier to work with and yet more powerful than WSDL. I suspect that the most important descriptive components of REST web services will be XML schemas (in whatever schema language).
Paul Prescod
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