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Re: Preconditions /effects vs Preconditions/Postconditions

From: Jos de Bruijn <jos.de-bruijn@uibk.ac.at>
Date: Mon, 15 Sep 2003 09:38:03 +0200
Message-ID: <3F656C5B.4000500@uibk.ac.at>
To: Monika Solanki <monika@dmu.ac.uk>
Cc: www-ws@w3.org
Dear all,

Here is a better quote from the WSMF document about what a 
post-condition is in terms of Web Services:

Post-conditions describe what a web service returns in response to its 
input.

A post-condition provides a declarative description of the relation that 
must hold between the input and the output of the service.
A limitation of DAML-S in my opinion is the limited of the effect. Since 
DL does not include variables, it is currently not possible to formulate 
the post-condition of the service in the DAML-S "effect".


Best,
Jos


Monika Solanki wrote:

> Short reply for now.
>
> I guess, we all are talking about the same thing. The difference is 
> maybe only in the way we put it across. Post condition is indeed the 
> condition which is true after service execution. However, in the 
> terminology that we use in DAML-S, an "Effect" may be  produced  under 
> certian condition and this condition is true only after service 
> execution, therefore this condition is the "Post condition". Quoting 
> from WSMF document:
>
> The pre-condition is the condition that has to be true
> for the input in order for the web service to be able to successfully 
> execute it. The postcondition
> is the condition that holds once the complex service has been executed
> successfully, i.e., it defines constraints on its output.
>
>
> Sheshagiri, Mithun wrote:
>
>>  
>>
>>     -----Original Message-----
>>     *From:* Monika Solanki [mailto:monika@dmu.ac.uk]
>>     *Sent:* Friday, September 12, 2003 6:18 PM
>>     *To:* Sheshagiri, Mithun
>>     *Cc:* 'Sheila McIlraith'; www-ws@w3.org
>>     *Subject:* Re: Preconditions /effects vs Preconditions/Postconditions
>>
>>
>>
>>     Sheshagiri, Mithun wrote:
>>
>>>I might be be wrong but I think Monika and Sheila are talking about two
>>>different conditions.
>>>
>>>Monika is talking about Effect of execution being a condition and this she
>>>terms as postcondition. 
>>>
>>     :-) .. Incidentally, by "Postcondition" , I mean precisely, the
>>     conditions under which the "effect" is produced and which is alos
>>     a subclass of ceCondition (which is also what Sheila is referring
>>     to), and not "the effect of execution being a condition".
>>     [Sheshagiri, Mithun] 
>>      
>>     I was under the impression that postcondition would be
>>     something that holds after the service is executed.
>>
>>     AtomicProces: BuyBook
>>     input: bookName
>>     precondition: validUser
>>     effect: points to disjointUnionOf(BookShippedEffect,
>>     BookWillBeShippedEffect)
>>     (BookShippedEffect, BookWillBeShippedEffect ) subClassOf
>>     ConditionalEffect
>>     BookShippedEffect
>>              +------ceEffect BookShipped 
>>              +------ceCondition BookImmAvail 
>>     BookWillBeShippedEffect
>>              +-------ceEffect BookWillBeShipped
>>              +-------ceCondition ¬BookImmAvail
>>      
>>     BookImmAvail determines the effect so is it correct to call it
>>     a postcondition?
>>
>>     On the other hand,
>>     The effect of executing an AtomicProcess might be the assertion
>>     of a condition. I thought this would be a postcondition
>>      
>>     AtomicProcess: ValidateCC
>>     input: CCname, CCnum, CCexpiry
>>     effect: points disjointUnionOf(ValidEffect, InValidEffect)
>>     (ValidEffect, InValidEffect) subClassOf ConditionalEffect
>>     ValidEffect
>>              +------ceEffect Valid
>>              +------ceCondition CreditApproved
>>     InValidEffect
>>              +-------ceEffect InValid
>>              +-------ceCondition ¬CreditApproved
>>     ValidP /sameValues/ Valid 
>>      
>>     Now  Valid and ValidP could be subClassOf process.owl#Condition
>>     and Valid is this case, IMHO,  is a postcondition. And since
>>     ceEffect can point to owl:Thing, this is permitted.
>>      
>>     phew! I need a program that generates names for my classes and
>>     properties.
>>      
>>
>>     --Monika
>>
>>>(ceEffect points to a concept which is a subclassof
>>>process:#Condition. And Sheila is talking about the condition being pointed
>>>by ceCondition which decides the effect.
>>>
>>>mithun 
>>>
>>>  
>>>
>>>>-----Original Message-----
>>>>From: Sheila McIlraith [mailto:sam@ksl.Stanford.EDU] 
>>>>Sent: Thursday, September 11, 2003 5:45 PM
>>>>To: Monika Solanki
>>>>Cc: www-ws@w3.org
>>>>Subject: Re: Preconditions /effects vs Preconditions/Postconditions
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>Monika,
>>>>
>>>>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,
>>>>    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.  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.
>>>>
>>>>As for what we need for WS composition, we need both the 
>>>>*effect* and the *condition*, but the *effect* is the key notion.
>>>>
>>>>Regards,
>>>>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 
>>>>    
>>>>
>>>>>document.
>>>>>
>>>>>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
>>>>>
>>>>>Thanks,
>>>>>
>>>>>Monika
>>>>>
>>>>>--
>>>>>**>><<**>><<**>><<**>><<**>><<**>><<**>><<**
>>>>>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
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>    
>>>>
>>>
>>>  
>>>
>>
>>     -- 
>>     **>><<**>><<**>><<**>><<**>><<**>><<**>><<**
>>     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
>>     **>><<**>><<**>><<**>><<**>><<**>><<**>><<**
>>
>
> -- 
> **>><<**>><<**>><<**>><<**>><<**>><<**>><<**
> 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
> **>><<**>><<**>><<**>><<**>><<**>><<**>><<**
>

-- 
Jos de Bruijn

Institute of Computer Science
University of Innsbruck
Technikerstraße 13
A-6020 Innsbruck
Austria
 
Tel:      +43 512 507 6475
Fax:      +43 512 507 9872
Email:    jos.de-bruijn@uibk.ac.at
Homepage: http://homepage.uibk.ac.at/~c703239/

Next Web Generation research group
http://www.nextwebgeneration.org/
Received on Monday, 15 September 2003 03:38:14 GMT

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