W3C home > Mailing lists > Public > public-ws-chor@w3.org > January 2004

Re: choreographies implementation

From: Steve Ross-Talbot <steve@enigmatec.net>
Date: Sun, 18 Jan 2004 21:33:15 +0000
Message-Id: <ECDD31C3-49FD-11D8-977C-000393D13C9A@enigmatec.net>
Cc: <public-ws-chor@w3.org>
To: "Guadalupe Ortiz" <gobellot@hotmail.com>

Dear Guadalupe,

See comments inline ...


Steve T

On 17 Jan 2004, at 18:18, Guadalupe Ortiz wrote:

> Dear Steve, before of anything, thank-you very much for your help.
> I will try to be clearer in my questions or in the things I didnt 
> understand very well.
> Ive been reading a lot of different documents about choreographies 
> and I think I have rmore or less the most important ideas, but there 
> are still some things that are hidden for me
> Why did you say that WSCI is just history? I mean, I know its a 
> Sun... proposal for choreographies, and I think its being studying by 
> the W3C WS Choreography Group. The goal is to get an standard similar 
> to W3C or is there any better/newer proposal.
> I think too, please help me to clarify, that BPEL4WS is more for 
> orchestation thna choreographies and that there is not interest in the 
> W3C for studying it to be an standard.

WSCI was only a working note that gave rise to the formation of the W3C 
Web Services Choreography working group. As such it was never and has 
never been a standard. In has been informative, as has BPEL4WS and as 
has BPML, on the workings of the working group. But it would certainly 
be wrong to think that WSCI defines what the group is doing. It simply 
does not. What the group is doing has some relation to WSCI but WSCI 
did not have the same scope as the Choreography working group has set 
down. All in all it is better to think in tems of WSCI as interesting 
history and not something that is current.

Yes BPEL4WS is more for orchestration. But abstract BPEL4WS (as per 
V1.1) was attempting to describe external observable behaviour of a 
single web service. What it did not and does not do is look at the 
wider picture - which is necessary for interop when you think about it 
- which is very much a notion of a global model (something that WSCI 
does talk about but does very badly). The global model is very much 
what Web Services Choreography is all about.

> About the access point Ill try to ask my question with an example. 
> Suppose the tipical example with the traveler agent web service, the 
> airline company web service and the rent car company web service. You 
> want to make a choreography with them.
>   * you have the wsdl from the three parties and the wsci (or other 
> interfaz for choreographies)  from the three parties. OR IS THE WSDL 
> * If you have any of that posibilities, its suposed that you have too 
> an WSCI of the global model (are the other embebed in this one?)
> * Now, what I mean about the access point, If I want to invoquee any 
> operation of the choregraphy, do I invoque it in the global model or 
> do I have to search the WSDL from the parti to invoque it?

As to the access point ... If a CDL (Choreography Desciption Language) 
describes the external observable behaviour of a global model, then it 
does not have to execute. All that needs to be done is to buy a vendor 
product that can read the CDL file for a specific model and use it in 
conjunction with your web services that acts as a participant. In this 
way the CDL file with the vendor tool can provide runtime behavioural 
type checking to ensure that the participants abide by their 
contractual behaviour as set down in that CDL file. Thus the notion of 
an entry point does not have the same meaning for a CDL.

It maybe the case that some company using this sort of technology (when 
available) wishes to join some form of exchange based on web services 
connecting and exchanging information. All they need to do is get a 
hold of the appropriate CDL file(s) and use a vendor tool to ensure 
that they also conform to the contractual behaviour defined in the CDL 
file. Alternatively they could use a tool that reads in the CDL file 
and generates the approriate WSDL descriptions and code skeletons for 
them. They are then free to embellish those code skeletons as they see 
fit. They might try to integrate an existing web service with the 
skeleton to ensure consistency and interop are achieved.

> Just one question more. If  now want to create a ws choreography, I do 
> know, supossly, how to specify it in XML (according one standard 
> candidate as WSCI). I specify it and then? How do I try it? Is there 
> any software or any idea? Should I translate it to a programing 
> language?

No software is available at this time. We have only got a requirements 
spec thus far, a base language spec is well on the way to being 
available for public review and we do (in our charter) have to 
implement tools (and so software) that uses this stuff. So expect 
things to happen over the next 3-6 months.

> Thank very much for all your help, Im really greatfull

Hope all this helps.


Steve T
Received on Sunday, 18 January 2004 16:33:52 UTC

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