- From: Ricky Ho <riho@cisco.com>
- Date: Fri, 11 Apr 2003 10:25:08 -0700
- To: Assaf Arkin <arkin@intalio.com>, steve@enigmatec.net
- Cc: "'Cummins, Fred A'" <fred.cummins@eds.com>, "'Burdett, David'" <david.burdett@commerceone.com>, jdart@tibco.com, public-ws-chor@w3.org
+1 Rgds, Ricky At 09:49 AM 4/11/2003 -0700, Assaf Arkin wrote: >Steve Ross-Talbot wrote: > >>I'd like to echo Fred's comments. I think external is the way to go and >>if we can provide "compatibility" as a minimum and "verifiablity" as a >>nice to have we would have done a great job. >> >>The notion of "observable behaviour" and the associated "bi-simulation" >>are in essence how we should approach the issue of verfiability. We want >>to ensure that "contracually" the external behaviour defined (allowable >>message patterns over given states) is the observably equivalent to any >>implementation. It doesn't matter if the implemetation is done over >>BPML, Java, BPEL or even by people. If we can observe it as equivalent >>then we can say it bi-simulates the externally defined behaviour and so >>meets the contract. >> >>One issue I am less sure on is the issue of time. If observable >>behaviour is allowable message patterns over given states, what role >>does time play in all of this? Does it have a role? Thoughts ..... >> >The basic premise is that you treat everything as events and you find a >way to agree on the occurrence of events. This also ties the choreography >to other models the express everything in terms of events (e.g. various >distributed and consensus algoritms). > >There are two ways you can agree on an event occuring. By communicating >the event itself or by communicating the condition that leads to that >event. And there are two ways you can communicate that stuff: by sending >messages (events) or by agreeing to use a particular choreography (a form >of communication in itself). > >An event like 'order completed' is explicitly communicated from seller to >buyer. An event like 'order completed notificiation time-out' is fired >internally by each service, but the fact that this event will occur at the >same time for both buyer and seller is communicated, e.g. as part of the >purchase order message, or by agreeing to participate in the same >choreography. By agreeing in one way or the other when the time-out would >occur, both buyer and seller are synchronized with each other, even if >they don't exchange messages to signify the event. > >This is much like the real world. In the real world I can call you and say >"your order has completed" (possibly leaving you a voice mail) and we both >know the order has completed. Or I can call you and say "if you don't >reply by 5pm, the order is canccelled". If it's after 5pm and you didn't >call me, we can both conclude the order has been cancelled. There's no >need for a second confirmation. > >arkin > >>Cheers >> >>Steve T >> >> >
Received on Friday, 11 April 2003 13:25:31 UTC