W3C home > Mailing lists > Public > public-ws-chor@w3.org > December 2004

Reassertion of the request for clarification on short circuit evaluation

From: Tony Fletcher <tony_fletcher@btopenworld.com>
Date: Fri, 10 Dec 2004 10:40:33 -0000
To: <public-ws-chor@w3.org>
Message-ID: <001301c4dea4$ae2e01b0$6701a8c0@corp.choreology.com>
Dear Colleagues,
I am aware that we have already discussed this issue, but on reflection I
would like to re-assert my comment in clarifying with short circuit
evaluation of Boolean conditions is mandated or prohibited.  The reason is
given below followed by the comment.
Short circuit evaluation of Boolean conditions does not alter the value of
the condition but in CDL it can alter the time at which that condition
evaluation becomes available, which in turn can alter the evolution of a
choreography.  My concern is that if different endpoint projections make the
opposite assumption then erroneous behaviour could result.
Consider a Boolean condition of the form  Variable>100 AND
not exactly the correct syntax I am sure but hopefully you see the point.
With this condition as the value of a guard and block =true and assuming the
variable value is available immediately and is such that Variable>100 is
FALSE then if short circuit evaluation is mandated then the condition
evaluates to FALSE immediately and the choreography moves on.  However, of
short circuit evaluation is prohibited then the condition evaluates to FALSE
only after two hours has elapsed - very different behaviour in time and as
other interactions may also be time dependent we have to remember that CDL
can yield descriptions with some dependency on time.
Therefore: (!!)
1)  Rationale: Short circuit evaluation of Boolean conditions should be
explicitly allowed or disallowed so that different tools, endpoint
projections, etc do not make contrary choices of how to evaluate.


Add to section 2.4.3 Expressions (or elsewhere if a better place can be


Boolean conditional expressions MUST use short circuit evaluation techniques
whatever the setting of the block attribute.  That is once the value of a
conditional expression can be evaluated and the result will no longer change
if further variables become available or time based functions become true,
the conditional expression returns its value.


Note:  If it is thought this incorrect and we should not permit short
circuit evaluation for some good reason then we should specifically prohibit
it and add text similar to that above but stating MUST NOT instead.


Best Regards     Tony
A M Fletcher
Cohesions  (TM)
Business transaction management software for application coordination
www.choreology.com <http://www.choreology.com/> 
Choreology Ltd., 68 Lombard Street, London EC3V 9LJ     UK
Tel: +44 (0) 1473 729537   Mobile: +44 (0) 7801 948219
tony.fletcher@choreology.com     (Home: amfletcher@iee.org)
Received on Friday, 10 December 2004 10:41:04 UTC

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