He writes, in response to posts by Dave Rosenberg and Adam Fields:

A good first step would be a well-accepted service description language for HTTP-based Web APIs. WSDL doesn’t work in RESTian services and there’s no RESTful alternative. Moreover, most people don’t even see the need. Well, read Dave and Adam’s posts–there’s the need staring you in the face. The only way that we’ll get to a place where Web 2.0 apps are more easily integrated is when we have a service interface description language and other metadata standards for RESTful services.

I agree, and have something to propose: the LID, OpenID and XRI digital identity technologies are REST-ful. When we needed to have additional metadata around those REST-ful services to accomplish interoperability and intermediation — just like the case that Phil describes —, the people from these three initiatives jointly constructed the Yadis metadata discovery framework to solve this issue.

.

Yadis is a general-purpose mechanism by which "service types" can be associated with service URIs, such as RESTful identity URLs. It works just fine for digital identity purposes, and there is no reason to assume it wouldn’t work for other purposes. In fact, during Yadis design, we were very concious of the fact that there may be many other applications areas for Yadis that have nothing to do with identity, and Phil’s requirements are examples for those.

And if you think Yadis is not expressive enough, you can always add more meta-data through XML namespaces.

P.S.: I’d love to hear feedback if you use Yadis for purposes other than identity.