WS-ReliableMessaging and WS-Addressing are public!


Here's BEA's, TIBCO's, IBM's and Microsoft's take on how to do reliable messaging on web services. There are more than subtle differences compared to the "WS-Reliability" spec by NEC, Sun, Oracle, etc: WS-ReliableMessaging is extensible, takes WS-Security and WS-Policy into account and it does not have (less is sometime more) any specific transport bindings -- and it's routable (read on).

I will likely write about a couple of observations later, but here's a little "reading guide" for a single sentence in section 3.1 saying "There MUST be no more than one <Sequence> element in any message". That language is a bit confusing an could be worded a bit better, because what it really says, when read having SOAP 1.2's "role" or SOAP 1.1's "actor" model present in your mind is indeed "There MUST be no more than one <Sequence> element targeted at one role in any message".

That's because in the presence of roles, all headers become technically "invisible" to any but the targeted role and there is indeed never more than one <Sequence> element existing in the message as far as a certain role is concerned. It'd be helpful if the language was a bit clearer there, but SOAP actually takes care of enabling roles for this, even in the presence of that sentence.

Why are roles relevant? Because this now enables reliable delivery in the presence of routing intermediaries, which want to establish reliable links between them. If you have A->B->C->D with reliable messaging being used for the end-to-end connection A->D and the hop B->C shall be individually outfitted with reliable messaging for purposes of optimization, you can do that by specifying roles on an additional <Sequence> that applies to B and C.