W3C home > Mailing lists > Public > public-ws-chor@w3.org > April 2003

Re: Feedback on Glossary

From: Assaf Arkin <arkin@intalio.com>
Date: Tue, 22 Apr 2003 19:28:30 -0700
Message-ID: <3EA5FA4E.5050702@intalio.com>
To: "Cummins, Fred A" <fred.cummins@eds.com>
CC: "Monica J. Martin" <monica.martin@sun.com>, public-ws-chor@w3.org

Cummins, Fred A wrote:

>Monica,
>
>Feedback on the glossary,
>
>Composition.  [This definition is becomeing much too complicated.  How
>composition is addressed in choreography is to be defined by the final
>specification.  What we mean 
>by composition should be quite simple: creation of a unit or product from
>components or parts.  There is an implication that the components or parts
>may be used to compose a variety of units or products.  To extend this to
>choreography, composition is the creation of a choreography from parts that
>may be used to create a variety of choreographies.]
>  
>
The term composition is very generic and I wanted to point out that it 
can be used for many different things. Let's say that I have two states, 
one in which I accept an order and one in which I send a shipping 
notice, and a transition between the two. The combination of all three 
is a composition.

I found it very helpful to use the term composition in many different 
places. For example, a process definition is a heirarchical composition 
of activities. But since a process can use other processes as well, it's 
also a recursive composition. A global model is defined easily as a 
composition of interfaces/service types that are linked to each other. 
The idea is that you can decompose these interfaces/service types and 
then recompose them into other choreographies (reuse).

While composition is a very generic term (X+Y=Z), and so is recursive 
composition (X(a)+X(b)=X(c), there are more specific types of 
compositions that we are interested in. I think we need to spell them 
out and properly qualify them.

For example, a recursive service composition is a composition of 
services (be it a choreography, orchestration or just a shopping list) 
that results in a new service. A recursive choreography composition is 
the ability to take multiple choreographies and compose them into a 
larger choreography. A choreography itself is a composition but it may 
not be recursive, it may be the composition of elements of other types 
(e.g. interfaces, services, message types, etc).

I definitely agree with your definition:

To extend this to choreography, composition is the creation of a choreography from parts that
may be used to create a variety of choreographies.

My friendly amendment would be to rephrase it as:

A choreography is a composition created from parts that may be used to create a variety of choreographies.

But I think that the definition of composition by itself should either 
be generic to allow for any other types of compositions we care about 
(now and in the future), or that we can just rely on the dictionary 
definition but define specific qualified types of compositions we care 
about in the glossary.

arkin
Received on Tuesday, 22 April 2003 22:30:09 UTC

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