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Re: Preconditions /effects vs Preconditions/Postconditions

From: Monika Solanki <monika@dmu.ac.uk>
Date: Thu, 11 Sep 2003 18:45:18 +0100
Message-ID: <3F60B4AE.3050908@dmu.ac.uk>
To: www-ws@w3.org
Sheila McIlraith wrote:

>In DAML-S we are able to express conditional effects.  These are
>the side effects of a web service, as contrasted with its output.
>E.g.,  AcmeBookSeller Web Service:
>  *output* is purchase receipt
>  *conditionalEffect* is comprised of a *condition* and an *effect*
>    the *effect* is that the book is sent to the customer,
 I am wondering how would this effect be captured at a lower level of 
abstraction than an ontology. I understand that conditions can be 
captured as logical formula ( This is also mentioned in Process.owl). 
Would the effect be a formula as well ? In that case, the complete 
definition of a conditional effect would be a conjunction of "condition" 
and "effect" , which has to be used for the composition.

>    under the *condition* that the book is in stock.
>Side effects of services are critical to encode for the purposes of
>automated WS composition, where such effects must be considered in
>composing and executing services.  (Something we humans do all the time.)
>As to how this relates to the wschor document you were reading, it would
>be helpful to have the citation, but without seeing it, here is a
>general answer.  
I apologise, I should have mentoined this earlier.

Web Services Choreography Requirements 1.0

>In the AI planning literature the term "effect" is often
>used synonymously with the term "postcondition".  It is used
>generically to captures the notion of effects which are either conditional
>(i.e., conditional effects) or unconditional.
>I'm guessing that ws-chor's notion of "postcondition" is used in this
>context.  It is possible that they have done away with the notion of
>condition in their "postcondition", because this is simpler, but I would
>argue, is not sufficiently expressive to capture the true side effects
>of web services.
My understanding was they have just the "condition" as "Post condition" 
and not the "effect"

>As for what we need for WS composition, we need both the *effect*
>and the *condition*, but the *effect* is the key notion.
>Sheila McIlraith
>On Thu, 11 Sep 2003, Monika Solanki wrote:
>>In DAML-S we have Preconditions and Effects(Conditions and Effect).
>>BPEL4WS does not have the notion of Preconditions and Postconditions( to
>>the best of my knowledge). However the ws-chor group  have defined
>>Precondition and Postcondition for the use cases in their requirement
>>I am wondering if the semantics of the "Conditions" for "Effects" as
>>defined in DAML-S are different from "Post conditions" in ws-chor doc,
>>as  what we are really interested in is the condition itself.  What
>>would be lost (just for the sake of argument) if we were to discard the
>>notion of "effect" and retain only the condition part of "Effect" i.e if
>>I may call it,  "Post condition". I say this because I feel that in some
>>way the effect part gets reflected in the output. Maybe "Effect" makes
>>it more explicit. I guess even for service composition, what we are
>>really interested in apart from input -output is the conditions that are
>>captured in Preconditions and Effects. I guess what I am really trying
>>to say is can we simplfy the notion of Conditional effects by
>>attributing it as "post condition" without compromising anything that is
>>not covered in any other property parameter.
>>Any comments / thoughts well appreciated
>>Monika Solanki
>>Software Technology Research Laboratory(STRL)
>>De Montfort University
>>Hawthorn building, H00.18
>>The Gateway
>>Leicester LE1 9BH, UK
>>phone: +44 (0)116 250 6170 intern: 6170
>>email: monika@dmu.ac.uk
>>web: http://www.cse.dmu.ac.uk/~monika
>*** Moving to Dept. Computer Science, University of Toronto ***
>Sheila McIlraith, PhD                 Phone: 650-723-7932
>Senior Research Scientist             Fax:  650-725-5850
>Knowledge Systems Lab
>Department of Computer Science
>Gates Sciences Building, 2A-248       http://www.ksl.stanford.edu/people/sam
>Stanford University                   E-mail: sam-at-ksl-dot-stanford-dot-edu
>Stanford, CA 94305-9020
Received on Thursday, 11 September 2003 13:39:11 GMT

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