Web Things, by Mark Baker

Clemens has some doubts and questions about REST, which I’m more than happy to respond to.

What I don’t get together is the basic idea that “every thing is a uniquely identifiable resource” with the bare fact that the seemingly limitless scalability of the largest websites is indeed an illusion created by folks like those at Akamai, which take replicated content around the globe and bring it as close as possible to the clients

I’ve heard this objection several times. What I always point out, is that REST is explicitly layered, and that the Web is scalable because Akamai and other solutions like it, can exist.

Taken to the last consequence of every data facet being uniquely identifiable through a URI (which it then should be and is) this model can’t properly deal with any modification concurrency.

Not true. There are many known means of dealing with concurrent access to data, and the Web has a good one; see the lost update problem (though other solutions may be used too). The one described in that document is actually a very well designed one too, as other solutions have problems with “hand of god” centralization issues (e.g. round identifiers).

While this solution only addresses concurrent access to an individual resource, WebDAV offers some useful extensions for dealing with collections of resources, and concurrent access to them.

So, what are the limits of data granularity to which REST applies? How do you define boundaries of data sets in a way that concurrency could work in some way […]

REST’s level of data granularity is the resource, but a resource can be a collection of other resources, as WebDAV recognizes.

and how do you define the relationship between the data and the URI that identifies it?

By use; the data returned by GET over time determines what the URI identifies. Though in the case a resource that’s created by PUT, then the one who’s doing the PUTting already knows, since they’re directly effecting what GET returns.

So to sum up, I too believe that REST has places where it’s useful, and places where it’s not, and that there will be other useful systems deployed on the Internet which are not built around REST or REST extensions. But I don’t believe “Web services” will be amoungst them, because the current approach fails to recognize that being built around a coordination language is essential to any Internet scale system.