- From: Furniss, Peter <Peter.Furniss@choreology.com>
- Date: Thu, 22 May 2003 15:03:21 +0100
- To: "Mark Little" <mark.little@arjuna.com>, "Bob Haugen" <rhaugen@speakeasy.net>, <public-ws-chor@w3.org>, "Ricky Ho" <riho@cisco.com>
Mark replied: > > Mark Little's message distinguished a "two-phase coordination > > protocol" case from a "lightweight correlation" case. I > don't believe > > these are genuinely different - in implementation, they are just > > alternative partitionings of the same work and, in message > > exchange/protocol terms, OASIS BTP was specifically designed to do > > both. (WS-T isn't currently quite as flexible) > > They are different precisely the manner I outlined (though > perhaps didn't give enough text): the latter case does not > require a separate coordinator as its functionality may very > well already be built into the business logic. We are working > with companies that do not need a separate coordinator (or > transaction) service whether that is based on BTP or WS-T: > they have spent many years on developing in-house management > systems that do this for them and do it very well (and in the > presence of failures). ok - if the point was the separate coordinator. But the "separate coordinator" may be just a separate object in the same process. That's quite orthogonal to the message exchange between the client-side as a whole and the service-side as a whole, which you also showed as different. > > > Actually, I'm especially intrigued that Mark doesn't count that as > > being "two-phase". > > You are correct and wrong: firstly this is a two-phase > approach; secondly I did not say it wasn't two-phase in my > original email! Sorry - you identified the first explicitly as two-phase, and I thought that was part of the distinction. > > There's obviously a double exchange, and it's clear the > service passes > > through a "doubt phase", where it's waiting on the leftside > to confirm > > (or presumably, cancel) the order. To me, that's two-phase > - there's a > > request for work to be performed contingent on a later yes/no, then > > the yes/no. Whether there's an explicit prepare signal, or > whether the > > coordinator could be separated (or, as here, is integrated on the > > left-side) are particulars that don't affect the principal. > > Again, correct. However, in this case it's two-phase, but > there are situations where it isn't and BTP (since I'm > assuming you're pushing that) isn't appropriate. Not exclusively BTP, but every coordination case we've come across seems to end up with the contingent, then yes/no phases. Using that as the defining characteristic of two-phaes, are there really others ? Or is it a question of terminology, that a more restrictive (and no doubt useful) definition of two-phase would give a different classification. Peter
Received on Thursday, 22 May 2003 10:03:33 UTC