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RE: resend: Updated Choreography concept/relationship proposal

From: Martin Chapman <martin.chapman@oracle.com>
Date: Fri, 11 Jul 2003 11:21:44 -0700
To: "Champion, Mike" <Mike.Champion@SoftwareAG-USA.com>, <www-ws-arch@w3.org>
Message-ID: <PEEBJKKCFNCENDPJDEMIGEOPDGAA.martin.chapman@oracle.com>

Mike,
one main comment:

>The most
> appropriate
> formalism for an orchestration appears to be the pi calculus, whereas the
> most appropriate formalism for a choreography appears to be the event
> calculus.



> -----Original Message-----
> From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On
> Behalf Of Champion, Mike
> Sent: Thursday, July 10, 2003 7:57 AM
> To: www-ws-arch@w3.org
> Cc: Champion, Mike
> Subject: resend: Updated Choreography concept/relationship proposal
>
>
>
>
> XXX Choreography
> XXX.1 Definition
> A Web Services Choreography is a formal model of the pattern of
> possible web
> service invocations among a set of service providers and consumers.  The
> choreography must specify the set of messages that may be sent, the set of
> publicly observable states that each participant in the
> choreography may be
> in, and the transitions from one state to another to be expected upon
> receipt of the defined messages.  There is no requirement that the parties
> literally implement the shared state machine described by the
> formal model,
> only that the choreography provides an abstract description of
> the sequence
> of legal interactions and their consequences.
>
> XXX.2  Relationships to other elements
>
> A choreography defines the pattern of possible interactions
> between a set of
> SERVICES
>
> The primitive interactions in a choreography are MESSAGE EXCHANGE PATTERNS
>
> A choreography may be expressed in a CHOREOGRAPHY DESCRIPTION LANGUAGE.
>
> XXX.3 Discussion
>
> SOAP and WSDL by themselves can describe only very simple Web services
> consisting of a single interaction between a consumer and provider pair.
> The SOAP Recommendation formally specifies only two MEPs,
> "Request-Response"
> and "SOAP Response."  Web Services Choreography is the subject area
> describing web services interactions involving more than two
> parties and/or
> more than one operation.

I would say at least two parties

>
> A choreography is model of the sequence of operations, states, and
> conditions which govern  composite web service.

Given recent discussions in chreo about web service composition vs choreo
composition maybe change compisite to "linkages beteen" or something like
that.

>Successfully following the
> pattern of interaction prescribed by a choreography should result in the
> completion of some useful function, for example: the placement of
> an order,
> information about its delivery and eventual payment, or putting the system
> into a well-defined error state.


>
> A choreography is not to be confused with "orchestration".
> Orchestration is
> the defintion a series of web service invocations from a single single
> party's point of view (the "conductor", and is generally deterministic;
> whereas a choreography is the global view of the interactions among
> autonomous parties and is generally non-deterministic.

I dont see any evidence either way for determinsm and non determism in
either approach!

>The most
> appropriate
> formalism for an orchestration appears to be the pi calculus, whereas the
> most appropriate formalism for a choreography appears to be the event
> calculus.

This is not accurate or agreed wrt choreography and event calculus. Pi is
equally suitable.
Without starting a huge debate, I would propose that this sentence is
deleted. I dont see what it adds.



>
>
> YYY Choreography Description Language
> YYY.1 Definition
> A Choreography Description Language is a notation for describing a
> choreography.  It may also permit the specification of a composite service
> in terms of component services.

What are component services?

>
> YYY.2 Relationships to other elements
>
>
> A choreography Description Language describes the pattern of allowable
> interactions between a set of services
>
>
> A choreography Description Language describes the conversations possible
> between service requesters and service providers.
>
> A choreography description language much be minimally capable of formally
> describing the interactions in known Message Exchange Patterns.
>
>
> YYY.3 Discussion
> A Choreography description language is a formal, machine-processable
> definition of a specific choreograpy.  A choreography descripion language
> formally defines the message exchange pattern(s) used by a web
> service.  It
> permits the description of how Web services can be composed, how roles and

change composed to inter-linked?
> associations in Web services can be established, and how the
> state, if any,
> of composed services is to be managed.
>
>
> WSBPEL is an "orchestration" language in WSA terminology whereas BPSS is a
> "choreography" language.

do we need to mention these two - or a least include others.


>
>
Received on Friday, 11 July 2003 14:21:27 GMT

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