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Subject: NEW ISSUE: Semantics of offered Sequences



Title: Semantics of offered Sequences

Description:

The current specification explains how a RM Source may offer a Sequence to the RM Destination, but does not explain what this really means. It can be read as a protocol optimization, with no deeper semantics. It could alternatively be assumed that the 2 sequences are linked in some way - perhaps application replies are expected to travel back on this sequence (and no other); perhaps the offered Sequence is supposed to close/terminate when the other Sequence closes/terminates. Someone might even assume that offers will only be made for request-reply applications, wheras the absence of an offer implies fire-and-forget messaging. (I am not advocating this interpretation!)

We should clarify the specification, so that the reader is fully aware of the semantic import of offering (or accepting the offer of) a Sequence.

Justification: The capabilities in the spec should have clear semantics

Target: core

Type: design

Proposal:
I think that we should clearly state that there is no deep semantic to offering a Sequence, it is merely a protocol optimization. I think that the right way to explain that is to add a note into the text that introduces offer, saying that the use of offer is semantically identical to not using offer, and then initiating another Sequence between the two endpoints. Describing this is a little tricky, as we don't want to talk about creating a Sequence from RM Destination to RM Source.... and we don't have a term in the spec for the middleware layer that implements RM in either direction. Here is a concrete proposal:


Add the following as a continuation of line 256 (using line numbers from wsrm-1.1-spec-wd-06.pdf):
Note, offering a Sequence within the <wsrm:CreateSequence> element is simply a protocol optimization. There is no semantic difference between offering a Sequence, and choosing not to offer one and subsequently creating a Sequence to carry messages from the Ultimate Receiver to the Initial Sender.

Related issues: None

Thanks

Matt
--
Matt Lovett, WebSphere Development
Email: mlovett@uk.ibm.com
Phone: 248310 (internal), +44 (0)1962 818310 (external)



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