RE: Preconditions /effects vs Preconditions/Postconditions

Hi Walden,
 
For the first part. You're exactly talking about a credit card payment while
the original scenario should be with debit card. 
As for the failure, I think we're trying to illustrate it from the
application viewpoint instead of specific process modeling. 
Yinsheng Li  

> 
> > -----Original Message-----
> > From: Walden Mathews [mailto:waldenm@optonline.net]
> > Sent: Monday, September 15, 2003 2:43 PM
> > To: Charlie Abela; Li, Yinsheng
> > Cc: www-ws@w3.org
> > Subject: Re: Preconditions /effects vs Preconditions/Postconditions
> > 
> > 
> > 
> > How about this:
> > 
> > The post-condition of a (successful) credit card transaction
> > is that your loan balance is increased and your available credit
> > is decreased, both by the transaction amount.
> > 
> > (An invariant on the account state is that current balance
> > plus available credit always = credit limit, but that's a little
> > outside the scope here.)
> > 
> > The effect of a (successful) credit card transaction is the
> > existence of a new transaction identifier, which is handed to
> > you as an outcome of the operation.
> > 
> > Failure states are not part of the post-condition or effect
> > landscape.  In other words pre- and post-states are part of
> > the model of successful operation.
> > 
> > How does that fly?
> > 
> > Walden Mathews
> > 
> > 
> > ----- Original Message ----- 
> > From: "Charlie Abela" <abcharl@keyworld.net>
> > To: "Li, Yinsheng" <Yinsheng.Li@nrc-cnrc.gc.ca>
> > Cc: <www-ws@w3.org>
> > Sent: Monday, September 15, 2003 1:04 PM
> > Subject: RE: Preconditions /effects vs Preconditions/Postconditions
> > 
> > 
> > > IMHO, the distinction between the post-condition and 
> effect is not a
> > > clear-cut distinctionme definitions that I found for 
> > "post-condition" over
> > the web:
> > >
> > > i. The post condition is a statement of what the world 
> > should look like
> > > after an operation. For instance if we define the operation 
> > square on a
> > > number the post-condition would be of the form result = 
> > this * this (where
> > > result is the output and this is the object on which the 
> > operation was
> > > invoked). The post condition is a useful way of saying what 
> > we do, without
> > > saying how we do it, separating interface from implementation.
> > > ii. Post Condition: State of the system after executing the 
> > operation.
> > > iii. A post-condition specifies some facts about the world 
> > which can be
> > > expected to be valid after the service operation has finished its
> > execution
> > > regularly.
> > >
> > > As for the defined example I'd say that the distinction 
> could become
> > clearer
> > > if:
> > >
> > > Post-condition: credit card billed/not billed
> > > Effect: transaction successful/failed
> > >
> > > Charlie
> > >
> > > -------------------------------------------------
> > > Charlie Abela
> > > Research Student,
> > > Dept. of Computer Science and AI
> > > University of Malta,
> > > MSD06. Malta
> > > Web: http://www.semantech.org
> > > Email: abcharl@keyworld.net
> > >
> > > -----Original Message-----
> > >
> > >
> > >
> > > All email is scanned by Keyworld against known Viruses. 
> > This service is
> > offered to all Keyworld subscribers and hosted domains and 
> > does not carry
> > any warranty. You are advised to protect your PC with updated 
> > antivirus
> > software at all times.
> > >
> > 
> > 
>

Received on Monday, 15 September 2003 15:35:04 UTC