In the Last Call version of the WS-Choreography specification several
exchange elements are allowed in an interaction element.  One is the request
going in one direction and the others must be in the reverse direction
(though is that rule stated explicitly?).  Only one of these is allowed to
be the 'normal' response message, all the others must be fault messages.
 
The case I am particularly interested in seems to be supported by neither
WS-Choreography at present nor WSDL 1.1 and I wonder if it should be.   (I
understand that WSDL 2.0 could support what I propose as an extension,
though I plan to make a comment into the WSD group with the aim of making it
a standardised feature.
 
 Suppose I have request - response protocol pair but there can be several
distinct response messages.  So I want to say the request message is A and
the response is B or C (or possibly fault message X or Fault message Y). 
 
I realise that of course you can write it as five (in this case) one way
interactions, but that looses the request response semantic.  You could also
re-write the protocol to only use a single response message and internally
to the response message have different parameter values that give the
semantics of B or C - and likewise one can re-write the Fault message to
combine X and Y, but why should one have to change the protocol to suit
WS-Choreography?
 
I would like to be able to write, for example, something like: 
<interaction name="ABCF" channelVariable="tns:aChannel" operation="a"> 
      <participate relationshipType="SuperiorInferior"
fromRole="tns:Superior" toRole="Inferior"/> 
      <exchange name="A" informationType="Atype" action="request">
              <send variable="tns:A"/>
              <receive variable="tns:A"/>
       </exchange>
       <exchange name="B" informationType="BType" action="respond">
              <send variable="tns:B"/>
              <receive variable="tns:B"/>
        </exchange>
        <exchange name="C" informationType="CType" action="respond">
              <send variable="tns:C"/> 
              <receive variable="tns:C"/>
        </exchange>
        <exchange name="F" informationType="FType" action="respond">
              <send variable="tns:F" causeException="true"/>
              <receive variable="tns:F" causeException="true"/>
        </exchange>
</interaction>
 
 I would be quite happy to have some sort of explicit 'choice' construct
around the multiple responds that are regular permitted responses and
therefore do not have cause exception set, or an implicit choice as we
currently have for multiple exception causing responses.

 

Best Regards,

Tony