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RE: Global view requires transactions (RE: Use Cases )

From: Furniss, Peter <Peter.Furniss@choreology.com>
Date: Thu, 22 May 2003 15:03:21 +0100
Message-ID: <221369570DEDF346AE42821041345E89194D90@exchange1.corp.choreology.com>
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 GMT

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