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RE: Requirements Objection: Machine Processable Control Logic

From: Ugo Corda <UCorda@SeeBeyond.com>
Date: Fri, 18 Jul 2003 15:27:32 -0700
Message-ID: <EDDE2977F3D216428E903370E3EBDDC908124A@MAIL01.stc.com>
To: "Yaron Y. Goland" <ygoland@bea.com>, "WS Chor Public" <public-ws-chor@w3.org>


I don't fully understand your dislike of XPath. I can use XPath to select particular logic portions of a message part (as defined in a WSDL portType/interface) and still make no commitment to how those logical portions map to the actual message on the wire. The concrete mapping is only specified by the WSDL binding.


> -----Original Message-----
> From: Yaron Y. Goland [mailto:ygoland@bea.com]
> Sent: Friday, July 18, 2003 2:33 PM
> To: 'WS Chor Public'
> Subject: Requirements Objection: Machine Processable Control Logic
> Non trivial control logic requires both externally visible 
> inputs (messages)
> and internally visible inputs (local variables, databases, 
> etc.). If WS-Chor
> only supports specifying control logic based on externally 
> visible inputs
> then WS-Chor will be unable to express the equally critical internally
> visible inputs to a decision and so will specify incorrect logic.
> Of course WS-Chor could choose to specify both the internal 
> and external
> inputs, which would necessitate the creation of a full 
> fledged programming
> language which would require duplicating the work BPEL is 
> doing. I would
> suggest we are best advised to leverage their work than to 
> duplicate it.
> More generally, non trivial control logic changes over time. 
> However the
> whole point of web services is the idea of loose coupling 
> which means in
> this case that control logic should be able to change within 
> fairly wide
> parameters without having to change the behavior of partners. 
> By explicitly
> specifying control logic in a machine readable form we freeze 
> the control
> logic used by a participant since any changes they make will break
> assumptions their partners have made based on seeing what 
> their logic looks
> like. This is why I believe that in the majority of cases WS-Chor
> specifications won't have accompanying BPELs since in most 
> cases specifying
> the BPEL would be counter productive as it would 'over 
> specify' things. Put
> more generally, in most cases specifying control logic in any machine
> readable form (XPATH) causes choreographies to become 
> unnecessarily fragile
> and is hostile to the goal of interoperability.
> This is why I object to including requirements to specify 
> control logic in
> machine processable format, even if we restrict the control 
> logic to only
> addressing externally visible inputs.
> 		Yaron
Received on Friday, 18 July 2003 18:27:54 UTC

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