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RE: MEP proposal

From: Assaf Arkin <arkin@intalio.com>
Date: Mon, 24 Feb 2003 11:45:40 -0800
To: "Amelia A. Lewis" <alewis@tibco.com>, "Jacek Kopecky" <jacek@systinet.com>
Cc: <www-ws-desc@w3.org>
Message-ID: <IGEJLEPAJBPHKACOOKHNGEOKDDAA.arkin@intalio.com>



> -----Original Message-----
> From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org]On
> Behalf Of Amelia A. Lewis
> Sent: Monday, February 24, 2003 8:34 AM
> To: Jacek Kopecky
> Cc: arkin@intalio.com; www-ws-desc@w3.org
> Subject: Re: MEP proposal
>
>
> I think that it is perfectly possible for the WSDL to describe a
> single role, which is always the advertised service, and which is
> (typically; see note 1 below) a single node.  The fact that the
> WSDL tends to describe a single node which is taking on the
> role(s) specified by the service description does not, to my
> mind, mean that the service description MUST describe every
> interaction that this particular node has with all other nodes,
> whatever their roles.

+1

> note 1: another of the things that adds to the confusion for
> message exchange patterns is that a service could easily be
> defined, using a multicast target address, as a distributed sort
> of application.  That is, the service description could easily be
> describing a cooperating set of nodes, all playing the "service"
> role.  This is a lot easier than it sounds, but only if you're
> familiar with pub/sub and multicast.  Again, I haven't raised
> this as an issue because it's what the textbooks call "an
> advanced topic", and isn't, I think, necessary to think about
> deeply while resolving the issue of message exchange patterns.

In that case there are multiple services that all share the same end-point,
essentially, a common channel, but still one service role. The only
difference is that the input will be processed multiple times and you may
receive multiple responses (assuming some communication idiom that supports
that).

So you look at such communication idiom as involving a group with:

- Indefinite number of clients (but one role) but any communication
originates from one client
- Indefinite number of servers (but one role) but any communication involves
one channel (end-point) shared by all servers
- Description is given from the point of view of the service where service
denotes the listener on that channel, but is not strictly one server
- Communication idiom identified as multicast implying multiple responses vs
unicast implying single response

(I still can't think in terms of more than two roles for the communication
idiom, but can definitely see multiple roles in the choreography ;-) )

note 2: I have suggested looking at group communication before as the model
for WSA for that same reason. Even if we don't consider this advance topic
as interesting at this point in time, at least we can talk in more abstract
terms to allow its introduction in the future. End-point as a channel for
communication is more interesting than end-point as a URL for accessing a
server.

arkin


>
> Amy!
> --
> Amelia A. Lewis
> Architect, TIBCO/Extensibility, Inc.
> alewis@tibco.com
Received on Monday, 24 February 2003 14:47:43 GMT

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