services and roles

I am noodling on services again.

The following diagram is intended to capture a particular view of 
services: the factoring of messages into different aspects (potentially 
represented by different headers) and different roles that combine into 
a single service.


It seems to me that the concept of a role is the key analog of headers, 
for services. I don't much like abusing the word; but the essence is 
(to me) that a service role represents a stakeholder in the processing 
of a message. Different aspects of a message might be represented with 
SOAP headers; (or combinations of them or some other property).

Thoughts? Anyone listening?
Frank