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Re: OWL-S process preconditions

From: Dónal Murtagh <domurtag@cs.tcd.ie>
Date: Fri, 18 Jun 2004 17:09:48 +0100
Message-ID: <015501c4554e$adb77cf0$053fe286@pc1568>
To: "Bijan Parsia" <bparsia@isr.umd.edu>
Cc: <public-sws-ig@w3.org>, <www-ws@w3.org>

On Jun 18, 2004, at 10:00 AM, Dónal Murtagh wrote:

> Greetings,
>
> My understanding is that OWL-S does not currently mandate any language
> for
> expressing preconditions, although the current frontrunner is SWRL.

OWL-S 1.1 will, by default, make use of conjunctions of SWRL (like)
atoms. It will allow for other preconditions languages (like KIF).

I didn't realise there is an OWL-S 1.1, the latest release listed at
http://www.daml.org/services/owl-s/ is 1.0. Any idea where I can find
information about this new version?

> For example, assume we have a book-buying process which takes an input
> CreditCardDetails (among others) and has a precondition
> CreditCardValid.
> Evaluating the truth of this precondtion could (for example) involve
> testing
> whether the credit card number has the correct format and whether the
> expiry
> date is later than the current date. In order to perform this test we
> need 3
> pieces of information:
>
> 1.    credit card number
> 2.    expiry date
> 3.    current date
>
> The first two could be characterised as 'external' in that they are
> provided
> by the user/agent invoking the process via the input parameter
> CreditCardDetails. Is it true to say that all such external information
> required to test a precondition must be obtained from the process'
> inputs,
> or can one assume that other information sources are available?

There is a presumption that there is a knowledge base -- e.g., a
planner's "state of the world" -- against which preconditions are
evaluated and effects applied. That kb could do infogathering on
demand, I suppose.

Sure, but my question is really about what is initially in the KB, is it
just that information which the invoking agent has explicitly supplied (to
the process)?

> My second question is about how to express such a precondtion via
> SWRL. The
> most common use for SWRL rules seems to be moving property values from
> one
> individual to another,

> But how should one express a precondition such as described above in
> SWRL
> syntax? Assuming CreditCardDetails has properties which provide the
> necessary information (e.g. CreditCardNumber, ExpiryDate), then
> presumably
> these could be used in conjunction with the SWRL built-ins to
> establish the
> truth of the precondition, buth what would appear as the consequent
> (RHS) of
> the rule?

Nothing. We don't use swrl conditionals, only swrl atoms and
conjunctions.

A precondition is a conjunction of swrl atoms commonly evaluated
against the state of the world before the process executes and which
must be true in that state for the process to succeed (or, perhaps, to
be invoked).

OK, so a precondition should be expressed as a conjunction of SWRL atoms,
rather than a SWRL rule (with an antecedent and consequent). By the way, are
there any examples available of SWRL being used to express process
preconditions (or indeed any other OWL-S conditional expressions)?

Best Wishes,
Dónal
Received on Friday, 18 June 2004 12:10:53 GMT

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