So the other shoe has dropped, and Yaron Goland has just given some background on Microsoft's draft Web3S protocol, while Dare comments. Which seems at first glance kind of interesting and certainly could expand the field of REST based services in a big way. At the same time, I'm confused by some of the stated rationales for not extending APP the way GData does. I think there are some straightforward answers to each of the gaps he identifies:
Turtles all the way down:
<feed> ... it's turtles all the way down! ... </feed>
I think this is orthogonal, but there's already a proposed extension to APP: Partial Updates. Which uses (revives?) PATCH rather than inventing a new verb or overloading PUT on the same resource. I'm neutral on the PATCH vs. POST or PUT thing, except to note that it's useful to be able to 'reset' a resource's state, so having the ability to allow this via either two verbs or two URIs is useful too. I'm a little confused though since Yaron says that they're using PUT for merging but they're also defining UPDATE as a general purpose atomic delta -- so why do you need to overload PUT?
I need to think about the implications of extending the semantics of ETags to cover children of containers as well as the container.
I do like Web3S's ability to address sub-elements individually via URIs; APP provides this out of the box for feeds and entries, but not for fields within an entry. It's not difficult to imagine an extension for doing so that would fit seamlessly within APP though.
I think it'd be interesting to look at an APP+3S (APP plus 2-3 extensions) to see how it would compare against Web3S, and whether the advantages of a stable, standard base do or do not outweigh the disadvantages of starting from something not tailored for your solution. Certainly the issues raised by Yaron are fairly generic and do need solutions; they're not new; and the thinking of the APP WG has pretty much been that these sorts of things are best dealt with via extensions.