[Issue 2] Proposal version 3: How to implement SCA callbacks usingSOAP

Attached.
I have converted the HTML version to Word, so that it is easy for folks 
to comment and make inline changes.

The big change between v2 and v3 is the addition of faults. My initial 
inclination was to define our own faults, but it turns out WS-Addressing 
has some pre-defined faults which fit our purpose. So, I have reused 
those faults.

One thing I'm not clear on is whether the TC wishes to define this 
SOAP-specific callback mechanism as *one* of the ways callbacks can be 
implemented when using SOAP or *the* way callbacks are implemented when 
using SOAP. My inclination is to say *the* way, otherwise we have to 
invent ways (metadata such as policySets, ws-policy assertion, WSDL 
extension, Java annotation) to convey when it is required.

Comments?

-Anish
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