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Re: Issue on Boolean conditions

From: Gary Brown <gary@enigmatec.net>
Date: Thu, 28 Oct 2004 14:45:39 +0100
Message-ID: <002f01c4bcf4$6db5f560$0200a8c0@LATTITUDEGary>
To: "Tony Fletcher" <tony_fletcher@btopenworld.com>, <public-ws-chor@w3.org>, "Public-Ws-Chor-Request List" <public-ws-chor-request@w3.org>

Good point Tony.

I have a related question regarding lexical ordering, concerning the order of type definitions. For example, the channel attribute defined in the 'passing' element of the ChannelType element. Should this only be able to reference a channel type that has previously been declared in lexical order i.e. can a type be referenced before it has been declared?

We probably need some generic statements that clarify these situations.

  ----- Original Message ----- 
  From: Tony Fletcher 
  To: public-ws-chor@w3.org ; Public-Ws-Chor-Request List 
  Sent: Thursday, October 28, 2004 11:41 AM
  Subject: Issue on Boolean conditions

  Dear Colleagues,

  I do not think the current CDL specification ( Web Services Choreography Description Language Version 1.0  W3C Working Draft 12 October 2004  http://www.w3.org/TR/2004/WD-ws-cdl-10-20041012/  ) specifically states this, and perhaps it should, but I assume that a Choreography Description, written using CDL is to be interpreted element at a time in the sequence those elements are written down following the normal rules of XML documents (lexical ordering), except were the defined semantics of an element so encountered dictates otherwise - particularly the parallel and choice constructs in the case of CDL (not quite sure why we need sequence as that is the default ordering).

  Following on from this idea one naturally assumes that conditionally expressions are evaluated when (and only when) they are encountered.  This rule would seem to apply well to the guard attribute which is evaluated when a work unit element is encountered.  However, it does not apply if we want the same guard condition to be re-evaluated at any later point (as the current text implies rather confusingly).  The current text in place seems to state that the repetition condition is also evaluated on entry to the work unit.  It is not clear to me that this is useful and it would seem better to state (as implied elsewhere) that the repetition condition is evaluated when the work-unit is completed and before going on to the next element / step to see if the work unit should be repeated.  The text should state that once a repetition condition on a work unit has been tested and found to false (maybe after several previous evaluations that evaluated to true) then that work unit is left behind and not used again.

  The 'complete' attribute on the choreography element does not seem to fit this pattern at all and so it should be clearly specified  when it is evaluated (at a particular point, at several points, continuously while the choreography is active), and what happens when it evaluates to false, and what happens when it evaluates to true.

  Asking whether a choreography is complete as you start it seems a little odd, and asking the same question at the point the choreography element is complete and the description is about to end or go onto the next step seems even odder.  So it should be clearly specified  when it is evaluated and what happens when it is evaluated.

  Best Regards     Tony
  A M Fletcher
  Tel: +44 (0) 1473 729537   Mobile: +44 (0) 7801 948219
   amfletcher@iee.org       (also tony_fletcher@btopenworld.com)
Received on Thursday, 28 October 2004 13:46:07 UTC

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