Tim Bray proposes SMEX-D, yet another alternative to WSDL.

Two things I immediately don’t like: * The insistence on request/response — while this is the most popular MEP, it is by no means the only one. * Describing SOAP header schemas together with the “business” message - this should composable, orthogonal concepts.

And of course, Tim should take a look at the SSDL work.