The BASE of CREST

Yesterday WICSA 2009 finished. There were a number of interesting talks over the three days of the conference. One was by Richard Taylor on Architectural Styles for Runtime Software Adaptation. He was discussing a framework (BASE) for comparing approaches to dynamic runtime adaptation. The model classifies how various architectural styles deal with Behavior, Asynchrony, State, and Execution Context for adaptation.

One of the frameworks being analysed with BASE was CREST – Computational REST. In CREST, pieces of computation are represented as URLs and can be moved around the web just as static content is. Richard gave a demo of CREST in action – showing pieces of independent computation running and serving dynamic content to multiple distributed browsers. It certainly had a “wow” factor. It reminded me very strongly of the Google Wave demo. But CREST is a more general architecture – it’s not committed to the threaded content model that’s deeply built into Google Wave. Could you reimplement Google Wave on top of the CREST framework? It looks plausible, and it might also help you create and share a much richer variety of dynamic content – to put yourself ahead of the Wave (pun intended).

I had a few questions (some of which were prompted by discussions with Liming Zhu) but I didn’t get a chance to pin down Richard after the talk…

The first question is about CREST, but not BASE. We can observe that REST is “broken” on the web. For example, cookies aren’t part of (and violate!) the REST principles, but they are nonetheless essential to the workings of the Web. That’s fine – pragmatics will almost always get in the way of a naive realisation of an abstract model. So my question is – how (or if?) does CREST need to be “broken” for it to be workable?

My second set of questions is about the BASE framework discussed in the paper. What limitations do the various architectural styles carry on the scope of adaptation? How do you get assurance about invariant functionality? Why doesn’t BASE consider security? Dynamic adaptation is great, but not everything will be dynamically variable, and you probably want to know that some functionality won’t vary, and won’t be subverted at runtime. How do the various architectural styles enable that?