Roger Sessions on WS-*

Roger Sessions, noted architectural guru, author and Microsoft Architect MVP, has posted his latest newsletter on the WS-* family of specs. In typical Roger fashion, he decides to give them his own name – WS-SCRAM with SCRAM standing for “Secure, Coordinated, Reliable Async Messages”. (I forget where, but I once heard Roger refer to “three-phase transactions” instead of the relatively standard “two-phase commit transactions”.) Roger claims MS et. al. are pushing WS-STAR where “STAR” is an acronym standing for “Secure, Transacted, Async, Reliable”. Personally, I’ve never seen it written out like a an acronym and I always thought the * in WS-* was used as a wildcard, but it is true that we are focused more on transactions than coordination. On the Longhorn DevCenter, Indigo is described as providing “secure, reliable, and transacted messaging along with interoperability.”

This is actually the second time Roger’s taken on transactions in a web services architecture. His last newsletter on the topic had a much more detailed but harder to follow example. He points out that there are two related specs in this space – WS-AtomicTransaction and WS-BusinessActivity but that he thinks only WS-BA is going to work in the long run. WS-AT requires holding locks open in the DB, which is highly unlikely between services in different trust boundaries communicating with async messaging. Am I really going to lock the records in my database while I wait for a service that I don’t trust to figure out if it is able to commit or abort? I don’t think so. Pat’s wrote a great scenario showing how unrealistic the concept of long-running transactions really are.

However, at the end of the newsletter, Roger takes Indigo to task for implementing WS-AT and not WS-BA and I don’t agree with him. While I think WS-AT shouldn’t be used in web services architectures, Indigo is also responsible for moving existing technologies like COM+ forward. Leaving out WS-AT isn’t really an option in those scenarios. As for not implementing WS-BA, I’ve got to wonder just how valuable is WS-BA? While WS-BA avoids the DB locking issue of WS-AT, it still doesn’t deal with the delegation of control. WS-BA still leaves me beholden to the decision of some outside coordinator. This seems to violate two of Don’stenets of service orientation: “Boundaries are Explicit” and “Services are Autonomous”.