W3C home > Mailing lists > Public > www-ws@w3.org > September 2003

RE: Preconditions /effects vs Preconditions/Postconditions

From: Sheshagiri, Mithun <Mithun.Sheshagiri@hp.com>
Date: Fri, 12 Sep 2003 19:43:09 +0100
Message-ID: <5E13A1874524D411A876006008CD059F07383747@0-mail-1.hpl.hp.com>
To: "'Monika Solanki'" <monika@dmu.ac.uk>, "Sheshagiri, Mithun" <Mithun.Sheshagiri@hp.com>
Cc: "'Sheila McIlraith'" <sam@ksl.Stanford.EDU>, www-ws@w3.org
 

-----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
<mailto:sam@ksl.Stanford.EDU> ] 

Sent: Thursday, September 11, 2003 5:45 PM

To: Monika Solanki

Cc: www-ws@w3.org <mailto: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 <mailto:monika@dmu.ac.uk> 

web: http://www.cse.dmu.ac.uk/~monika <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
<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 <mailto:monika@dmu.ac.uk>  
web: http://www.cse.dmu.ac.uk/~monika <http://www.cse.dmu.ac.uk/~monika> 
**>><<**>><<**>><<**>><<**>><<**>><<**>><<**
Received on Friday, 12 September 2003 14:44:51 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 3 July 2007 12:25:44 GMT