AW: [service-orientated-architecture] Re: Orchestration, Choreography , and Composition

Mon, 24 Jul 2006 14:45:53 -0700

Sure, Ashley – here we go:

 

<orchestration name=P1>

  <sequence>

    receiveC

    sendA

    sendB

  </sequence>

</orchestration>

 

<orchestration name=P2>

  <sequence>

    receiveB

    receiveA

    sendC

  </sequence>

</orchestration>

 

P1 and P2 do not fit together: P1 wants to receive message C before sending out messages A and B. But messages B and A (in this order) are required by P2 in order to send out message C.  A typical deadlock situation.  Choreography can not help here.

 

The situation is a bit different in the following scenario: There are executions of P3 which will send out message B before message A – this is because <parallel> typically allows (!) to act in parallel but does not enforce to do so… In such executions, P4 will not be able to consume message B sent and, thus, neither message A.  A choreography may help here: By “wiring” P3.sendA with P4.receiveA and P3.sendB with P4.receiveB the environment hosting P3 can derive based on the ordering in P4 that it effectively has to send A before B. This way, a choreography, sometimes, can help making orchestrations fit together J

 

<orchestration name=P3>

  <sequence>

    <parallel>

      sendA

      sendB

    </parallel>

    receiveC

  </sequence>

</orchestration>

 

<orchestration name=P4>

  <sequence>

    receiveA

    receiveB

    sendC

  </sequence>

</orchestration>

 

There is an orthogonal discussion about how additional runtime QoS help to make orchestrations fit together: E.g. reliable messaging may buffer message B at site of P4 until message A is consumed by P4 and then pass B to P4 etc etc.



----- Ursprüngliche Mail ----
Von: Ashley at Metamaxim <[EMAIL PROTECTED]>
An: [email protected]
Gesendet: Samstag, den 22. Juli 2006, 20:55:36 Uhr
Betreff: Re: [service-orientated-architecture] Re: Orchestration, Choreography , and Composition

Frank wrote:
 
> The different how's (i.e. orchestrations) cannot always be woven together! They have to fit... Although there is
> quite some research going on these days on checking whether two orchestrations fit together, there will likely
> always be situation where that won't help.
 
Frank -- I am not sure what you mean by this. Can you provide a discussion or example of a case where orchestrations cannot be woven together? Or a reference to something that discusses this issue?
 
Thanks
Ashley

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