Which brings us to another sub-issue that Mark questioned: why do we need a way of identifying inferiors?

If the EPR mechanism has no means of communicating an application identity which can be understood, under some application contract, by both application elements (client/server, requester/responder or however you choose to model it), then it is not possible for the second method of checking to be supported, because the coordinator cannot present to the terminating application element a comprehensible view of the identity and number of the necessary inferiors. Note (in this respect) that a terminating application (the one that says "commit" in an ACID context) could legitimately exclude, rebuff or ignore unwanted or non-critical enlistments.

As I understand WS-Addressing, the reference properties are defined to be opaque to the receiver: in other words they must be represented as part of the address in back-communication, so that the publisher of the address can map the back-message (reply if you like) to an internal endpoint which "lies beyond" the ostensible transport end-point, but no reliance or interpretation can legimately be put upon these properties for application-level correlation.