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RE: Issue 1108 - proposal

From: Martin Chapman <martin.chapman@oracle.com>
Date: Mon, 20 Jun 2005 22:18:39 +0100
To: "'Steve Ross-Talbot'" <steve@pi4tech.com>, "'WS-Choreography List'" <public-ws-chor@w3.org>
Message-ID: <00b301c575dd$a4ce4190$0901a8c0@ie.oracle.com>

For some reason this seems to have fallen through the cracks so lets put
it on next weeks agenda.

Martin.

>-----Original Message-----
>From: public-ws-chor-request@w3.org 
>[mailto:public-ws-chor-request@w3.org] On Behalf Of Steve Ross-Talbot
>Sent: Tuesday, May 10, 2005 6:46 PM
>To: 'WS-Choreography List'
>Subject: Issue 1108 - proposal
>
>
>
>Martin,
>
>here is a possible way forward.
>
>Cheers
>
>Steve T
>
>Begin forwarded message:
>
>> Resent-From: public-ws-chor@w3.org
>> From: "Gary Brown" <gary@pi4tech.com>
>> Date: 20 April 2005 09:13:02 BST
>> To: <public-ws-chor@w3.org>
>> Subject: PROPOSAL related to: Example showing problem with current
>> isolation semantics in CDL
>>
>> We should clearly state in the spec that nested isolation
>> choreographies are not permitted.
>>  
>> Proposed Text:
>>  
>> Section 2.4.5 contains the following bullet point:
>>  
>> " When isolation is set to "true", changes to the Variable 
>information
>> MUST be visible for read or for write to its sibling Choreographies 
>> only after this Choreography has completed "
>>  
>> This should be extended to include the text:
>>  
>> "An isolated choreography cannot directly or indirectly perform
>> another isolated choreography."
>>  
>> Regards
>> Gary
>>  
>> ----- Original Message -----
>>  From: Gary Brown
>> To: public-ws-chor@w3.org
>> Sent: Tuesday, April 19, 2005 12:56 PM
>> Subject: Example showing problem with current isolation semantics in
>> CDL
>>
>> Hi
>>  
>> After the recent discussion on isolation being inherited from the
>> enclosing choreography, I wanted to outline the following example to 
>> show how simply changing the isolation attribute of an enclosing 
>> choreography can significantly change the behavior of the 
>> choreography.
>>  
>> <choreo A>
>>
>>     <variable name="var1" />
>>      <variable name="var2" />
>>     <choreo B isolation=true >
>>
>>         <assign value "x" to "var1" />
>>          <assign value "x" to "var2" />
>>     </choreo>
>>     <choreo C isolation=true >
>>
>>          <assign value "y" to "var1" />
>>          <assign value "y" to "var2" />
>>     </choreo>
>>  
>>     <parallel>
>>         <perform choreo B>
>>              <bind var1/>
>>              <bind var2/>
>>         </perform>
>>
>>         <perform choreo C>
>>              <bind var1/>
>>              <bind var2/>
>>         </perform>
>>     </parallel>
>> </choreo>
>>  
>> If choreo A is not isolated, then choreo B and C are 
>isolated in their
>> own right - and therefore because they are both accessing common 
>> variables, I assume that one or the other of the performs will wait 
>> until the other has completed - so in fact they will be performed in 
>> sequence. [If this assumption is not true, then I need to have an 
>> explanation of the behavior when two sub-choreos have the same 
>> isolated variable - at what point do they wait?]
>>  
>> Therefore the result would be that both variables would have the same
>> value - either 'x' or 'y' depending on the order in which the 
>> sub-choreos were actually performed.
>>  
>> However, if we now make choreo A isolated, the isolated 
>attribute on B
>> and C is now ignored, as the isolation is inherited from the parent 
>> choreography (as described at the last f2f).
>>  
>> This now means that because the variables 'var1' and 'var2' 
>are within
>> the same isolation scope, when the two sub-choreos are performed, 
>> there is no waiting/blocking. This means that the result of the 
>> overall choreography is non-deterministic, the variables could have 
>> any combination of 'x' or 'y'.
>>  
>> The problem is that a sub-choreography may be defined on the basis of
>> having isolation semantics - and this is effectively overridden when 
>> performed from an already isolated choreography. Whereas if nested 
>> isolation was supported, the semantics of the 
>sub-choreographies would 
>> be preserved, regardless of the isolation status of the enclosing 
>> choreography.
>>  
>> This example is showing a simple example, but in a real example the
>> isolation of a top level choreography could have unforeseen 
>> consequences on a sub-choreography that is many levels of nesting 
>> removed from the isolated choreography. A case of a small change 
>> having a significant impact on bahavior.
>>  
>> Regards
>> Gary
>
>
>
Received on Monday, 20 June 2005 21:18:13 GMT

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