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Subject: Re: [soa-rm-ra] Orchestration v. Choreography Discussion


Michael,

While I may know the neighbor service to invoke, that neighbor may perform its expected functions through one or more orchestrations.  I likely will not know how my neighbor actually performs its functions.

So I really think it goes both ways.

Ken

On Nov 28, 2007, at 6:54 AM, Poulin, Michael wrote:

To my knowledge, the relationship between orchestration and choreography is right opposite than stated in " in practice Choreography is composed of a number of Orchestrations taking place together. "
 
In the orchestration, an execution of multiple services is coordinated and managed by a mediating entity which calls the services in certain order; the services exchange messages with the mediating system primarily.(Some participating services may be composite services themselves engaging other services via orchestration, or choreography or directly)

In the choreography, each service knows exactly which neighbour service to invoke in the chain and how ( what message exchange has to be performed). That is, choreography is about explicit inter-service communication; it serves as a fragment of an orchestration.

In orchestration, the mediating system knows how to perform transformation, routing and exception handling. In choreography, all these are the service's responsibilities.
"Orchestration is akin to traffic lights where events are controlled centrally, whereas Choreography is more like a roundabout, where each participant is following a prearranged set of rules." - very well illustrates what I described. That is, orchestration is the traffic picture while choreography is a traffic element only. That is, an Orchestration  is composed of a number of Choreographies taking place together.
 
Cheers,
- Michael 

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From: Rex Brooks [mailto:rexb@starbourne.com]
Sent: 21 November 2007 20:30
To: Ken Laskey; Rex Brooks
Cc: soa-rm-ra@lists.oasis-open.org
Subject: Re: [soa-rm-ra] Orchestration v. Choreography Discussion

That's exactly what I thought, too.

Cheers,
Rex

At 3:19 PM -0500 11/21/07, Ken Laskey wrote:
I like the traffic light and roundabout example.  Works equally well with a 4-way stop sign in the US.

Ken

On Nov 21, 2007, at 2:56 PM, Rex Brooks wrote:

Hi Folks,

Before I needed to drop off, I heard what I could agree to as a working distinction between Choreography and Orchestration. Choreography is what takes place in Business Process Modeling of interactions (to some extent DesignTime work), and Orchestration is what takes place when actual Actions are triggered by some central conductor to produce Real World Effects (to some extent RunTime work). The distinction between RunTime and DesignTime does not hold since both can occur in realtime interactions that produce Real World Effects.  This was just another analogy.

I liked Frank's notion that in practice Choreography is composed of a number of Orchestrations taking place together. I would say taking place according to some agreed set of rules or parameters.

I looked on the web for better analogies than symphony composer or ballet choreographer doing Choreography and an orchestra conductor or ballet director doing Orchestration, and found:

"Orchestration is akin to traffic lights where events are controlled centrally, whereas Choreography is more like a roundabout, where each participant is following a prearranged set of rules."

http://blog.whatfettle.com/?p=247

Cheers,
Rex


--
Rex Brooks
President, CEO
Starbourne Communications Design
GeoAddress: 1361-A Addison
Berkeley, CA 94702
Tel: 510-898-0670



------------------------------------------------------------------------------------------
Ken Laskey
MITRE Corporation, M/S H305     phone:  703-983-7934
7515 Colshire Drive                        fax:        703-983-1379
McLean VA 22102-7508


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-- 
Rex Brooks
President, CEO
Starbourne Communications Design
GeoAddress: 1361-A Addison
Berkeley, CA 94702
Tel: 510-898-0670


-----------------------------------------------------------------------------
Ken Laskey
MITRE Corporation, M/S H305      phone: 703-983-7934
7151 Colshire Drive                         fax:       703-983-1379
McLean VA 22102-7508




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