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Re: Semantics of Preconditions and Effects

From: Sheila McIlraith <sam@ksl.Stanford.EDU>
Date: Wed, 27 Aug 2003 10:10:01 -0700 (PDT)
To: Monika Solanki <monika@dmu.ac.uk>
Cc: daml-process@bbn.com, www-ws <www-ws@w3.org>
Message-ID: <Pine.GSO.4.44.0308270958430.2938-100000@ksl.Stanford.EDU>


Hi Monika,

As you know, DAML-S enables the modeler to associate the following
properties with a process
- input
- (conditional) output
- precondition
- (conditional) effect

"inputs" and "outputs" should be obvious.  A "precondition" describes some
state of the world that must be true in order for the service to be
invoked.  "(condiitonal) effect" describes the side effect of the program.
E.g., if executing the amazon.com service has the side effect that a
book is shipped to the address provided, then this is encoded as a
"(conditional) effect".  Note it is conditional if the effect occuring
depends on some condition.

As we argued in the paper you referenced below, "inputs" and "outputs"
can be regarded as "knowledge preconditions" and "knowledge effects".
That is, they pertain to the agent (executors) state of knowledge.
If ISBN is the "input" to amazon, it is identical to say that the agent
must *Know* the ISBN number;  this is a knowledge precondition of the
process.  Likewise, if the "output" is the price of the book,
then it follows that the knowledge effect of the process is that the
agent *Knows* the price of the book.

So, to answer your question, the agent can have knowledge effects, but
they are encoded as and "output" of a process.  That is the way
the agent's state of knowledge is updated.  Note also that the agent
*Knows* all the effects of the process it is invoking, so it follows
that any "effect" is also a "knowledge effect".

Sheila McIlraith




On Wed, 27 Aug 2003, Monika Solanki wrote:

> Hi All,
>
> I am trying to understand the semantics of preconditions and effects .
> In one of the papers
>
> Narayanan, S. and McIlraith, S., "Simulation, Verification and Automated
> Composition of Web Services",
>
> I found that preconditions for any service can also be modelled as
> knowledge based apart from physical preconditions.For e.g: agent
> Knows(bookName) for a service like LocateBook. I am interested in
> knowing whether agent can have knowledge based effects as well for e.g:
> agent Knows(ISBN), especially for information providing services.
>
> Any thoughts appreciated.
>
> Cheers,
>
> 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
> **>><<**>><<**>><<**>><<**>><<**>><<**>><<**
>

==============================================================================

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 Wednesday, 27 August 2003 13:12:01 GMT

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