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

Re: Progressive Concreteness of Choreography binding

From: Assaf Arkin <arkin@intalio.com>
Date: Wed, 02 Apr 2003 14:21:12 -0800
Message-ID: <3E8B6258.8090206@intalio.com>
To: Ricky Ho <riho@cisco.com>
CC: public-ws-chor@w3.org

I am in support of the use of properties, but I don't understand the 
level of indirection or what it brings to the table.

Some properties are interesting to express in the context of a 
choreography. Rules that affect the flow (as given in this example), 
partners that are communicated, time-outs that are communicated (as 
opposed to pre-decided), etc.

Let's say that service seller X decides to extract the property in a 
very specific way that is different from how service seller Y extracts 
it. Any buyer would have to understand the different ways in which it is 
extracted in order to put that value in the message to begin with. So 
there's another level of complexity here that affects all the buyers.

It's much easier if you write the choreography such that all seller 
services (X, Y, future ones) would extract that information in much the 
same way, e.g. by referencing the abstract (not concrete) message. That 
allows all buyers to build their side of the choreography in a generic 
way because they understand the abstract requirements regardless of 
which specific service they end up talking to.

In practice, that's how I would write choreographies. Write only the 
abstract parts that do not depend on the specific service you end up 
using, so you can have one buyer that talks to any potential seller and 
vice versa. If I follow that best practice, I don't see any value for 
this level of indirection.

Comments?

arkin

Ricky Ho wrote:

>
> Continuing our discussion of "abstract message".  I want to show an 
> how we can start with a very abstract definition at the choreography 
> and progressively add concrete binding to that.
>
> Lets define a orchestration flow that is independent of message type 
> and only have the message properties concept.
>
> ABSTRACT PROCESS
> ===================
> At the very beginning, the process declares the "NAMES" of all 
> messages that it may send or receive.  It also declares the "NAMES" 
> and "TYPES" of message properties, but it doesn't say how the message 
> properties is extracted from the message.
>
> Within the process flow, it uses only the named "message" and "message 
> properties".
>
>
> Orchestration POHandlingProcess {
>     Partner declaration {
>         purchaser;
>         creditCheckProvider;
>     }
>
>     Message declaration { // all are "typeless"
>         PO;
>         POConfirmation;
>         PORejection;
>         CreditCheckRequest;
>         CreditCheckResponse;
>     }
>
>     Message Property declaration { // all are "typed"
>         float PO.dollarAmount
>         Customer PO.cust
>         Customer CreditCheckRequest.cust
>         int CreditCheckResponse.rating
>     }
>
>     Process {   
>         receive "PO" from partner "purchaser"
>         if ("PO.dollarAmount" > 100K) {
>             assign "PO.cust" to "CreditCheckRequest.cust";
>             send "CreditCheckRequest" to partner "creditCheckProvider";
>             receive "CreditCheckResponse" from partner 
> "creditCheckProvider";
>             if ("CreditCheckResponse.rating" > 3) {
>                 send "POConfirmation" to partner "purchaser"
>             } else {
>                 send "PORejection" to partner "purchaser"
>             }
>         }
>         send "POConfirmation" to partner "purchaser"
>     }
> }
>
>
> IMPLEMENTATION BINDING
> ======================
> The WSDL implementation binding basically map the partner into a 
> particular WSDL PortType.  Then it maps each named message (defined in 
> abstract process) into the WSDL PortType/Operation/Part (can be either 
> the request or the response).  Finally, it defines the message 
> properties in terms of XPATH which extract the data from the 
> corresponding message.
>
>
> Implementation Binding for "POHandlingProcess" {
>     Partner binding {
>         mySelf --> PortType POHandlingPT  // contains a one-way 
> "submitPO" operation
>         purchaser --> PortType POCallbackPT // contains 2 one-way 
> "confirmPO", "rejectPO" operations
>         creditCheckProvider --> CreditCheckPT // contains a 
> request/reply "check" operation
>     }
>
>     Message binding {
>         PO --> From request of (PortType = "POHandlingPT", Operation = 
> "submitPO", Part="po")
>         POConfirmation --> To request of (PortType = "POCallbackPT", 
> Operation = "confirmPO", Part="poConfirmation");
>         PORejection --> To request of (PortType = "POCallbackPT", 
> Operation = "rejectPO", Part="poRejection");
>         CreditCheckRequest --> To request of (PortType = 
> "CreditCheckPT", Operation = "check", Part="customerInfo");
>         CreditCheckResponse --> From response of (PortType = 
> "CreditCheckPT", Operation = "check", Part="Return");
>     }
>
>     Message Property binding {
>         PO.dollarAmount = XPATH(//totalAmount/@amount);
>         Customer PO.cust = XPATH(//customer);
>         Customer CreditCheckRequest.cust = XPATH(//customer);
>         int CreditCheckResponse.rating = XPATH("//rank");
>     }
> }
>
>
> PROTOCOL (ON-THE-WIRE-MESSAGE) BINDING
> ======================================
> This binding defines how the abstract message defined in WSDL is 
> serialized on the wire, such as which parts goes to SOAP header and 
> which goes to SOAP body.
> WSDL binding covers this.
>
>
> ADDRESS BINDING
> ================
> For dynamic address resolution, this defines the service provider 
> endpoint resolution mechanism.  For static address resolution, this 
> defines the actual service endpoint location.
>
>
> Rgds,
>
> Ricky



-- 
"Those who can, do; those who can't, make screenshots"

----------------------------------------------------------------------
Assaf Arkin                                          arkin@intalio.com
Intalio Inc.                                           www.intalio.com
The Business Process Management Company                 (650) 577 4700


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Received on Wednesday, 2 April 2003 17:22:29 UTC

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