RE: Intermediaries - various cases

Ugo,
 
I'd say in the case of store and forward that the intermediary is an incidental aspect of the MEP, meaning what matters is the ultimate destination, not whether intermediate queues may be involved along the way.
 
As you say, the case for pub sub is different.  I think the answer depends on whether or not the publish MEP is modeled separately from the subscribe MEP, or both publish and subscribe are part of the same MEP...?  Although even in the second case, it's not clear the publisher is an intermediary, at least not the same as other intermediaries (and was this Chris's point during the call?)
 
Eric

-----Original Message-----
From: Ugo Corda [mailto:UCorda@SeeBeyond.com]
Sent: Thursday, September 26, 2002 5:38 PM
To: 'www-ws-arch@w3.org'
Subject: Intermediaries - various cases



The discussion about intermediaries near the end of today's conf call reminded me of a couple of cases I have been thinking about in the context of queuing infrastructures.

Suppose I have a store-and-forward node to which I send SOAP messages to be forwarded to particular destinations. I specify the destination in an extension header, and I send the SOAP message to the store-and-forward node. The store-and-forward node receives my SOAP message and sends it to the final destination (possibly later, if the final destination is not available right away). It looks like in this case the Service Requester (according to our architecture diagram) is the node issuing the initial SOAP message, and the Service Provider is the final destination node. So the store-and-forward node must be the Intermediary.

But now let's think about a case where I have a publish-and-subscribe node. I send a SOAP message to that node with the intent that my message be distributed to any subscriber (I don't even know the address of those subscribers). So I send my SOAP message to the publish-and-subscribe node (the only node I am aware of) without specifying any final destination. In this case, is the publish-and-subscribe node still an intermediary, and are the destination nodes Service Providers? Or is the publish-and-subscribe node the Service Provider, which engages in separate interactions with the subscriber nodes? Or is there no single answer to these questions, and it all depends on the logical view that I want to apply to the scenario?

Ugo