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Re: Semantics of Preconditions and Effects

From: Monika Solanki <monika@dmu.ac.uk>
Date: Wed, 27 Aug 2003 18:34:12 +0100
Message-ID: <3F4CEB94.4060708@dmu.ac.uk>
To: Sheila McIlraith <sam@ksl.Stanford.EDU>
Cc: daml-process@bbn.com, www-ws <www-ws@w3.org>

Hi Sheila,

Thanks for your Reply.

Sheila McIlraith wrote:

>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".
So does it actually mean that these knowledge preconditions and effects 
are ineffect  manifestations of "input" and "output" and different from 
the actual preconditions and effects that we usually need for a DAML-S 
specification? I mean, can we actually use these knowledge preconditions 
and effects to specify the preconditions and effects of the service?

>Sheila McIlraith

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
Received on Wednesday, 27 August 2003 13:28:58 UTC

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