- From: Sheila McIlraith <sam@ksl.Stanford.EDU>
- Date: Mon, 15 Sep 2003 12:02:56 -0700 (PDT)
- To: Walden Mathews <waldenm@optonline.net>
- Cc: Charlie Abela <abcharl@keyworld.net>, "Li, Yinsheng" <Yinsheng.Li@nrc-cnrc.gc.ca>, <www-ws@w3.org>
Walden, Charlie, all, The terms "postcondition" and "effect" are not used consistently within the computer science literature. (Neither is the term "condition", for that matter, which appears to be conflated with "well-formed formula" in some of the email exchangtes.) While the distinction you make below may be a reasonable one, I don't think it reflects the use of *DAML-S* "effects" and *WS Choreography* "postconditions". The DAML-S Coalition will (I hope) discuss this offline on Wednsday and come up with a response to Monika Solaki's original question, which was to distinguish between these two uses of the terms. Regards, Sheila McIlraith On Mon, 15 Sep 2003, Walden Mathews wrote: > > 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. > > > > > ============================================================================== 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 Monday, 15 September 2003 15:03:34 UTC