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Re: Change of participants

From: Assaf Arkin <arkin@intalio.com>
Date: Tue, 22 Apr 2003 20:25:23 -0700
Message-ID: <3EA607A3.1010504@intalio.com>
To: "Cummins, Fred A" <fred.cummins@eds.com>
CC: Ricky Ho <riho@cisco.com>, public-ws-chor@w3.org

I briefly commented on that in the WSD or perhaps WSA (hard to keep 
track) ongoing discussion about using URIs to identify services.

I think that a service needs the concept of an address. The address can 
contain multiple points of contacts. For example, the service could say: 
use this URI between 5 to 9 and the other URI the rest of the time. Or 
use this URI if you can sign/encrypt messages and another URI if you opt 
to use SSL. So it should be able to represent an address that is more 
than just one URI, maybe by providing a WSDL service definition or 
something akin to WS-Addressing.

Perhaps a change of address could be addressed out-of-band using a more 
generic protocol that is not specific to the choreography, so all 
choreographies could leverage that capability without having to 
complicate all of them. Whether a buyer can allow the seller to change 
its point of contact midway through a choreography would depend on the 
use of this protocol, keeping the choreography simple.

But there's still needs to be some ability for a participant to be 
replaced at the discretion of all remaining participants, as per the 
choreography definition (i.e. the fact must be communicated to all 
affected parties). And also for the participant to be able to delegate 
responsibilities to other participants. For example, as a seller I may 
not be able to fulfill the order but I may delegate that to some other 
seller (by special agreement with that seller). Since that should occur 
at specific states and should not cover the buyer, it should be 
expressed in the choreography.

So these are three different use cases, and I think only the last two 
are something we should be addressing at some point.

arkin

Cummins, Fred A wrote:

>Assaf, Ricky,
>
>There is another dimension to changing participants assigned to
>roles.  The question is when can the entity behind the URI change. For
>example, it is possible that a participant wants to receive initial
>requests at one URI and redirect subsequent actions to different
>URIs, potentially depending on the nature of the request or
>the availability of resources.  The entity could be the same
>but the requests are directed to different processes or business
>units within the entity, or simply to different servers.
>
>>From a business standpoint, the participant sending the messages
>wants to know who he is dealing with.  Is it acceptable to have his
>messages redirected to a different entity?  I think this gets us into
>questions about the content and security of the messages, and beyond
>the scope of the choreography.
>
>A participant should be able to delegate to an "agent" to continue
>the exchange.  The delegation will require more than a simple "change
>of address."  The agent must be able to speak for the principal,
>and have appropriate credentials.
>
>So, I think dynamic changes to a participant (i.e., URI) assigned to 
>a role should be considered something quite acceptable at the 
>discretion of the participant.  It should make no difference in the
>choreography because the role remains the same. The message structure
>and content must provide for communication of such changes along with the 
>appropriate credentials to be associated with the new URI.
>
>Fred Cummins
>
>  
>
Received on Tuesday, 22 April 2003 23:27:00 UTC

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