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