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Subject: Re: [sca-assembly] Issue 5: Long-Running Request-Response Operations

I'll note that the SCA Policy FW spec already contains support for the
other relevant WS-A annotation/assertion:

   1431     NoListener – This intent may only be used within the @requires attribute of a         
            reference. It states                                                                  
   1432     that the client is not able to handle new inbound connections. It requires that the   
            binding and                                                                           
   1433     callback binding be configured so that any response (or callback) comes either        
            through a back-                                                                       
   1434     channel of the connection from the client to the server or by having the client poll  
            the server for                                                                        
   1435     messages. An example policy assertion that would guarantee this is a WS-Policy        
            assertion that                                                                        
   1436     applies to the <binding.ws> binding, which requires the use of WS-Addressing with     
   1437     responses (e.g. “<wsaw:Anonymous>required</wsaw:Anonymous>” – see                     
   1438     http://www.w3.org/TR/ws-addr-wsdl/#anonelement).                                      

Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093  or  8-295-6093

             Mike Edwards                                                  
             ibm.com>                                                   To 
                                       "OASIS BPEL"                        
             11/07/2007 05:37          <sca-bpel@lists.oasis-open.org>,    
             AM                        "OASIS Assembly"                    
                                       [sca-assembly] Issue 5:             
                                       Long-Running Request-Response       


(I am copying this email to Assembly as well as BPEL - I think there is an
Assembly issue lurking here that applies cross-language)

You are correct in saying that the behaviour sought is like that implied by
the NonAnonymousResponses assertion.

Another way of putting things, more in SCA terms, is that these sorts of
operations actually imply a Callback style of interface.

This is important, since it means, for example, that the initial request
operation by the client will complete without a response from
the service provider (as you say, there is an HTTP response but NOT a WSDL
response).  The response from the service
operation arrives later as a separate connection.  This is *precisely* the
idea behind callbacks and its asynchonous nature
is then "obvious" to the client, since there is a requirement to provide
the callback interface to get the WSDL response message.

OK, so far.

Client Implementation

The first implication for me is on the client programming API.  What is
described in WSDL terms as a Request/Response operation
is regularly mapped (using Java as the example) to a client API like:

SomeResponseMessageType response someOperation( SomeRequestMessageType
request ) throws OperationException1, OperationException2.

....but in the case of "long running" operations must be mapped to
something more like:

a)  void someOperation( SomeRequestMessageType request )


b)  void someOperationResponse( SomeResponseMessageType response ) throws
OperationException1, OperationException2

...where the client calls a reference with an interface including a) but
where the client must provide an interface including b).

There is also the need for a correlation between the original call to a)
and the callback on b).  This might be achieved through.
an ID being generated by the system when a) is called (would need to be
returned on the call), which can then be gathered from
the context when the callback is called.  Or it could be done in the now
"approved" asynchronous fashion for Java, by returning
a Future<type x> object from a) - and which would then implement the
interface b) and get called when the response message
arrives back at the client.

Service Implementation

The second implication for me is on the service implementation.  The
service implementation must know to "release" the protocol
stack which made the original service invocation, ideally rapidly after the
original request arrives.  There is then the need  for the
protocol stack to make a completely new connection when dealing with the
response message.

Now, this could be done via the Binding code - with the simple
call-and-return style preserved for the service implementation.
However, this may or may not be a sensible way of doing things.  The
alternative is that the service implementation takes the.
original request, gets a callback reference stores it and returns rapidly,
long before the operation is actually complete - the
callback reference is then used whenever the operation does complete
asynchronously.  The latter approach would use
the split interface style of a) and b) above.

WSDL and Interface handling

One way of approaching this then is to affect the interpretation of the

a) Let's assume that the WSDL operation is request/response

b) Let's assume that the WSDL operation is marked "long running" (some
annotation to this effect)

c) WSDL2LanguageX tools would have modified behaviour when encountering
this annotation and would generate
the "dual interface" mapping implied above.  Clearly this does not apply to
BPEL, which uses WSDL "native".

d) Clients and Providers in some native language would use the "dual
interface" form and construct their code
appropriately, in callback style.

e) If WSDL is used directly, then its interpretation by runtime and binding
code will be consistent with the interpretation
give here.

f) The WSDL annotation COULD be viewed as a Policy intent - it is just that
its implications go a bit further than selecting
an appropriate policyset  for the binding, since it affects the form of the
client and provider code.  This intent might
imply the WS-Policy assertion that Anish picks out, in the case of Web
services.  In the case of JMS and messaging
subsystems, things might be different (and simpler).


I hope that this helps in the debate - it is an interesting problem and a
common case once we deal with long-running
business processes.

Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431
Email:  mike_edwards@uk.ibm.com

 Anish Karmarkar                                                           
 01/11/2007 06:29                          Dieter Koenig1                  
                                           Danny van der Rijn              
                                           Re: [sca-bpel] NEW ISSUE:       
                                           Long-Running Request-Response   


Does the WS-Addressing WS-Policy assertion wsam:NonAnonymousResponses
[1] help here?

That assertion says that the effective ReplyTo and FaultTo EPRs must be
non-anonymous. I.e., reply is sent over a separate connection. That
means in the HTTP case, the HTTP response (not the WSDL response) to the
request is sent right away (relatively) and the WSDL response is sent in
a separate HTTP connection asynchronously to the non-anon ReplyTo.



Dieter Koenig1 wrote:
> Hi Danny, I cannot see where WSDL semantics would be changed. WSDL
> request-response operations do not make assumptions about any binding
> specifics, and in particular, about their response time and sync/async
> transport layers.
> BPEL processes have always been able to implement a WSDL r-r operation in
> way that may cause the response to be delivered significantly later.
> SCA clients attempting to synchronously invoke such operations will fail
> when the implementation returns control e.g. a month later. An
> SCA approach must be made available for clients interacting with such
> operations.
> The point of the issue is that clients invoking such operations first
> to be made aware about their long-running nature. With that, it can be
> decided that the usage of e.g. sync SOAP/HTTP bindings is not meaningful
> and other async means must be used to invoke the operation.
> Kind Regards
> DK

>   From:       Danny van der Rijn <dannyv@tibco.com>


>   To:         Dieter Koenig1/Germany/IBM@IBMDE


>   Cc:         sca-bpel@lists.oasis-open.org


>   Date:       26.10.2007 20:50


>   Subject:    Re: [sca-bpel] NEW ISSUE: Long-Running Request-Response

>       At this point in time, such long-running implementations of
>       request-response operations are NOT SUPPORTED by SCA.
> I'm not sure I understand this statement.  Why is it not supported?
> It seems to me (without fully understanding your proposal, I admit), that
> changing the semantics of a WSDL operation in the SCA-BPEL spec is out of
> scope.
> Danny
> Dieter Koenig1 wrote:
>       TARGET: SCA Client and Implementation Model Specification for
>       -
>       note that a resolution will likely affect other SCA specifications.
>       DESCRIPTION: Consider a WS-BPEL 2.0 process that implements a
>       containing a WSDL request-response operation, using an inbound
>       message
>       activity (<receive> or <pick>/<onMessage> or
>       <eventHandlers>/<onEvent>) and
>       a corresponding <reply> activity referencing this operation.
>       Furthermore,
>       assume that there are long-running activities between the inbound
>       message
>       activity and the <reply>.
>       At this point in time, such long-running implementations of
>       request-response operations are NOT SUPPORTED by SCA. As a result,
>       the very
>       first SCA-BPEL goal ("... use any valid WS-BPEL process definition
>       the
>       implementation of a component within SCA") is NOT MET.
>       Many concrete WS-BPEL scenarios involving such long-running
>       request-response behavior EXIST TODAY - long interrupts may be
>       by
>       timer-driven activities and service invocations bound to
>       protocols or involving user interactions. Many of these
>       processes expose request-response operations as this is a more
>       convenient
>       modeling style, for example, when the business logic is structured
>       hierarchies of parent and sub-processes. SCA must support using
>       processes as implementations of SCA components.
>       As an example, without loss of generality, consider the following
>       very
>       simple <sequence> containing a <wait> activity delaying the
>       by 14
>       days (of course, real-world processes would do useful work here
>       instead of
>       calling the <wait> activity :-).
>         <sequence>
>           <receive ... operation="rrOperation" .../>
>           <wait><for>'P14D'</for></wait>
>           <reply ... operation="rrOperation" .../>
>         </sequence>
>       The SCA implementation as well as a caller of this operation should
>       be made
>       aware of the long-running behavior. Note that inspecting the
>       implementation is not sufficient as the long-running nature of
>       activities
>       may not be visible in the process model. Regardless of the
>       of the
>       SCA assembly (component/service directly/transitively wired
>       within/across
>       composites), an SCA implementation would want to execute calls to
>       this
>       operation using some asynchronous means internally.
>       PROPOSAL: ********** To Be Discussed **********
>       A "longRunning" intent is introduced (policy-related details tbd.),
>       which
>       indicates the long-running behavior of an operation:
>         <operation name="rrOperation" ... requires="sca:longRunning"/>
>       Its runtime semantics are defined by the following naming
>       - a
>       request-response operation (with the "longRunning" intent):
>         <wsdl:operation name="rrOperation" ...>
>           <wsdl:input ... message="x:inputMessage"/>
>           <wsdl:output ... message="x:outputMessage"/>
>           <wsdl:fault name="fault1" message="x:fault1Message"/>
>           <wsdl:fault name="fault2" message="x:fault2Message"/>
>           ...
>         </wsdl:operation>
>       is executed AS IF it was specified as a one-way operation
>       the
>       request):
>         <wsdl:operation name="rrOperationRequest" ...>
>           <wsdl:input ... message="x:inputMessage"/>
>         </wsdl:operation>
>       AND a set of one-way callback operations (delivering the response
>       fault):
>         <wsdl:operation name="rrOperationResponse" ...>
>           <wsdl:input ... message="x:outputMessage"/>
>         </wsdl:operation>
>         <wsdl:operation name="rrOperationFault1" ...>
>           <wsdl:input message="x:fault1Message"/>
>         </wsdl:operation>
>         <wsdl:operation name="rrOperationFault2" ...>
>           <wsdl:input message="x:fault2Message"/>
>         </wsdl:operation>
>         ...
>       This naming convention enables an SCA implementation to execute a
>       long-running request-response operation in exactly the same way as
>       the
>       corresponding one-way operations defined in a bidirectional
>       interface.
>       All existing SCA means (Java APIs etc.) for bidirectional
>       can be
>       reused and no new APIs are required.
>       The following rules apply to SCA services and references:
>         (1) Attach a "longRunning" intent to a request-response operation
>       in a
>       component's service if and only if its implementation exposes the
>       long-running behavior described above.
>         (2) Attach a "longRunning" intent to a request-response operation
>       in a
>       component's reference if and only if its invocation exposes the
>       long-running behavior described above.
>         (3) Interfaces of references and services are considered
>       (eligible for wiring) if both sides match w.r.t. the "longRunning"
>       intent
>       on their contained operations.
>       Kind Regards
>       DK
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