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

Mon, 31 Jul 2006 01:10:26 -0700

Ash

Please may I suggest that you take your diagram, and draw a Y axis extending upwards from the bottom left hand corner.

Label it: 'composition'.

Then, on your diagram, you can write down what happens to each of 'objects', 'components' and 'services' when you compose them.  I think you'll find you get more objects, components, and services. 

This is because: The concept of composition is orthogonal to the concept of granularity.

You may then ask, where do processes fit into this?  Well, maybe that is down to your choice of 'process' semantics.  In any case, there will be a notion of composition there too.

alexis



On 7/27/06, ash galal <[EMAIL PROTECTED]> wrote:

Alexis
Composing two objects together as you descried, composes a component that might be used in one process as you said.
In SOA, when we build a process we might use orchestration engine to compose a process from different components or from only one component or, very rare, from object.
The Components or objects that the process is composed from is our starting point.
Level of granuality is very important here.
As Jeff Hanson stated is his article "Coarse-grained interfaces enable service composition in SOA" at http://builder.com.com/5100-6386-5064520.html
 

Figure A
Degrees of granularity
 
I think we start from higher level of abstraction than composing objects into component.
All the best
 
Ash Galal
 
 
 
 Alexis Richardson <alexis.richardson@gmail.com> wrote:
Ash

You are right that composing simple data objects into complex ones is possible - the ability to do so forms the basis for most OO programming.  Of course, each OO language has subtly different ways of encapsulating data and structuring interaction with it.

But composition is a general term and can mean other things too.  Here we are talking about composing different processes.  The question is what does composition mean here?  E.g. do different ways of describing processes leads to different - possibly new and challenging - notions of composition?

For example I might choose to implement two processes using OO, so that each process is associated with an (active) object.  I might 'compose' the objects into a larger, more complex, object.  Now, I have composed them according to your definition.   But is that all I that I have done?  No, because each object implements a behaviour and by encapsulating the two objects into one complex object, I may have forced the two objects to interact and form a new behaviour.  This new behaviour is a process, composed from the two primitive processes associated with the two objects. 

alexis
 






On 7/23/06, ash galal < [EMAIL PROTECTED]> wrote:
Hi Alexis
I think choreography is what and how too.
It covers two aspects: web service chorography interface and semantic web service chorography.
Web service chorography interface as described in W3C, is a specification and an XML-based language for describing interfaces used to specify the flow of messages at interacting web services.
Semantic web service chorography, deals with the description of the external message interface and conversational pattern exposed by a service that allow others to consume its functionality.
I think web service chorography definition covers semantic web service chorography definition too. I am confused a little bit in such definitions.
Semantic web service chorography could be considered as what while web service chorography interface is both what and how.
Composition is a result of combining simple objects data types into more complex data types or function calls into calling functions. I think it is low level than Orchestration.
Orchestration describes the automated arrangement and management of complex middleware or services.
Usually orchestration is an engine (how) often used for BPM, allowing developers to quickly orchestrate complex business processes involving multiple disparate systems.
 
Ash Galal

Alexis Richardson < [EMAIL PROTECTED]> wrote:
I don't know if this helps people to make a quick distinction, as it
is certainly a simplification :-) Nevertheless, one could say:

- the choreography is the 'what'
- the orchestration is the 'how'

It is very important to not confuse the what from the how.

I don't know what composition is, other than that two whats always
make another what, and two hows may make another how if sensibly
combined.

Cheers

alexis

On 7/20/06, Gervas Douglas < [EMAIL PROTECTED]> wrote:
> I think it would be really useful if we could reach some sort of a
> consensus on these definitions. "Orchestration" and "choreography" in
> particular are typical of terms which spring up into public discourse
> and then get bandied about as faddish terms, especially by markitechts
> and CBSOs, with most people not having a precise idea of their meaning.
>
> Gervas
>
> --- In [email protected], Teresa Jones
> <[EMAIL PROTECTED]> wrote:
> >
> > As a musician, I would say that all words are incorrectly used in IT....
> > However, I would perhaps try to define:
> > Composition - putting together 'services' to make a 'composite
> application'
> > - i.e. one that may then be fairly fixed for some time.
> > Choreography - the ability to sequence (loosely) services (which
> could be
> > human or computer) to be a business process.
> > Orchestration - probably the same as the above, but perhaps at a higher
> > level?
> >
> > Teresa
> >
> > _____
> >
> > From: Ashley at Metamaxim [mailto: ashley[EMAIL PROTECTED]
> > Sent: 19 July 2006 15:10
> > To: [email protected]
> > Subject: Re: [service-orientated-architecture] Orchestration,
> Choreography,
> > and Composition
> >
> >
> >
> >
> > Todd wrote:
> >
> > > I thought I'd turn this into a group exercise and see how all of you
> > > define it. (i.e., Orchestration, Choreography, and Composition)
> >
> > Excellent. This should be fun!
> >
> > In my view, Choreography defines a behavioural protocol to which
> multiple
> > parties must (or should) adhere when engaged in a service based
> > collaboration. I am sure that Steve R-T will give us the definitive
> > definition of Choreography!
> >
> > Like you, Todd, I am not clear whether there is any real difference
> between
> > Orchestration and Composition. Perhaps Orchestration is the means by
> which
> > Composition is achieved?
> >
> > Rgds
> > Ashley
> >
> >
> >
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