Re: Effects in OWL-S

Steve,
According to you, a postcondition is nothing but a logical consequence of
the frame axioms. This is not very useful.

Why would you want to specify a postcondition like that if it can be
derived by a reasoning system? Because of the limitations of the reasoning
system? 

In my view, a postcondition should be viewed as a constraint on the
after-state of an action, if the effect of the action is non-deterministic.


	--michael  


Battle, Steve writes:
>
> Here's another way of thinking about this - essentially from the situation
> calculus. An effect describes things that are true _because_ of an action,
> whereas, a postcondition describes things that are true _following_ an
> action.
> 
> Not everything that is true following an action is true because of it. A
> small example : If I add item A to my shopping trolley, then the effect is
> that "item A is in my trolley". If I then add item B to my trolley, then the
> effect is that "item B is in my trolley". Now, it's reasonable to assume
> that "item A is in my trolley" remains true because nothing I've done claims
> to effect the truth of it. So given that "item A is in my trolley" is a
> precondition of the "add item to trolley" action then "item A is in my
> trolley" is a reasonable post-condition, but not an effect. A lot of good
> work has gone into working out what post-conditions are reasonable given the
> effects (see the 'frame problem').
> 
> Steve
> 
> > -----Original Message-----
> > From: public-sws-ig-request@w3.org
> > [mailto:public-sws-ig-request@w3.org]On Behalf Of Charlie Abela
> > Sent: Wednesday, April 14, 2004 6:26 PM
> > To: Public-Sws-Ig@W3. Org
> > Subject: Re: Effects in OWL-S
> > 
> > 
> > 
> > With all these ideas going on about preconditions and effects 
> > in OWL-S it is
> > quite difficult to capture the general idea of how to define 
> > actual effects
> > in WSs.
> > 
> > I had the impression that an effect was something that will 
> > become true when
> > the WS has executed but that also brought some changes to the 
> > world, but now
> > there is talk of making use of post-condition instead. 
> > Actually from the
> > readings that I found, these two words seem to be used 
> > interchangeably,
> > depending on the research context, and thus I always presumed 
> > that they are
> > somewhat synonymous.
> > 
> > What are the views of the OWL-S ppl on this? Cause with all 
> > these somewhat
> > radical changes being proposed it is quite difficult to get people to
> > actually make use of these ontologies. Will there every be a 
> > stable set of
> > OWL-S ontologies?
> > 
> > Some time back there was a long discussion on the topic; I guess some
> > clarification is now due.
> > 
> > Regards
> > 
> > Charlie
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> 
>

Received on Monday, 26 April 2004 11:18:12 UTC