Mark Baker discovered our work on the Web Services Grid Application Framework (WS-GAF) and he thinks it's interesting. I am glad. We think our work from back in August was influential in all the recent changes in the Grid community world (i.e., making WS-RF Web Services-friendly and moving away from OGSI) although no one mentioned it in public.

Mark uses a quote from our paper that refers to REST. He's absolutely right in his comments. Since the original publication of that paper, Mark, Jim Webber, and I have had interesting conversations through private message exchanges on different topics. I really enjoyed them. It was through those message exchanges we realised that Mark was correct in that REST does not rely directly on HTTP.

We are currently working on a revised version of that paper which we hope to publish soon. We have already corrected that particular paragraph and we have acknowledged Mark for his help in better understanding REST. We were hoping to surprise him but he caught us first 🙂 Here's the paragraph as it stands in the current version. I hope it's more appropriate now...

There have been proposals for naming and uniformly providing access to resources, such as the REpresentational State Transfer (REST) [24] model. However, since REST depends on HTTP (or more accurately a protocol with HTTP-like semantics)¹ it is protocol specific and hence unsuitable for heterogeneous systems like the Grid. It also requires a particular interface to be used with the exposed resource, hence coupling identity and interface.

¹In practical terms, this means that HTTP proxies must be placed in front of non-HTTP aware resources (e.g. FTP).

I do hope this is closer to what REST is all about. Of course, we are prepared to further refine the above if necessary. I still stand with my assertion, though, that both REST and WS-RF couple identity, state, and interface and that's bad for the loosely coupled world in which we want to build applications. The Web works because of the sharing of standards like HTML and the flexibility of browsers in dealing with bad implementations of those standards. It is also the case that the human factor is involved, so broken links (coupling of identity and state) do not matter in many cases. When building distributed applications in such a world, we need something more. I think this is the gap that Web Services and SOA are trying to fill. Of course, I may be wrong. As always, I am interested in Mark's views.

(Note to self... must implement trackback. Perhaps this weekend.)