Choice of response message in WSDL

To the W3C Web Service Description Group,
 
[Please copy me directly on responses as while I am on the WS-Choreography
mailing lists I am not on the Web Service Description mailing lists - Thank
you.]


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.
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 2.0  and I wonder if it should be.   (I
understand that WSDL 2.0 could support what I propose as an extension,
though I make  this comment to 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
WSDL?
 
 In 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> 
 
and in the corresponding Web Service description  I would like to be able to
write something like:
<portType name="Requester">
     <operation name="abc">
          <output message="tns:A"/>
          <input message="tns:B"/>
          <input message="tns:C"/>
          <fault name="fault" message="tns:F"/>
     </operation>
</portType>
<portType name="Responder">
     <operation name="abc">
          <input message="tns:A"/>
          <output message="tns:B"/>
          <output message="tns:C"/>
          <fault name="fault" message="tns:F"/>
     </operation>
</portType>
 
or with explicit choice construct:
<portType name="Requester">
     <operation name="abc">
          <output message="tns:A"/>
          <choice>
              <input message="tns:B"/>
              <input message="tns:C"/>
         </choice>
          <fault name="fault" message="tns:F"/>
     </operation>
</portType>
<portType name="Responder">
     <operation name="abc">
          <input message="tns:A"/>
          <choice>
              <output message="tns:B"/>
              <output message="tns:C"/>
           </choice>
        <fault name="fault" message="tns:F"/>
     </operation>
</portType>
 
 I would be quite happy to have either 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                           


 <http://www.choreology.com/> 

Tony Fletcher

Technical Advisor 
Choreology Ltd.
68, Lombard Street, London EC3V 9L J   UK


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