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Re: the precondition property in OWL-S 1.0

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Sat, 8 Nov 2003 17:18:18 -0500
Cc: "Huhns, Michael" <huhns@engr.sc.edu>, public-sws-ig@w3.org
To: Monika Solanki <monika@dmu.ac.uk>
Message-Id: <74CC8BAD-1239-11D8-A350-0003936A0B26@isr.umd.edu>

On Saturday, November 8, 2003, at 11:10 AM, Monika Solanki wrote:

> Hi Michael,
> The property that makes it special does not lie in the syntax but in 
> the semantics. Precondition is a property which is required to be 
> true, before the execution of the service.

There's two aspects of a precondition, its own logical form, and the 
fact that it is embedded in larger conditional (effectively). So, if a 
precondition is that <<My Credit line is greater than 1000>>, the form 
of that assertion *could* just be a regular condition. and arguably 
should be. It's the *relationship* between that formula and the process 
that adds the extra semantics, much like putting a formula in the body 
of a rule "changes" its semantics (*if* it is co-true with the other 
atoms, then the consequential atoms must be true).

> So there could be several formulae that could be classified as 
> Conditions, however if any such formula is tagged with a qualifier 
> that it is a precondition, it makes a difference in the interpretation 
> of that Condition for the execution of the service.

I think having a precondition class such that it is a subclass of 
condition, and it is also a subclassof a someValuesFrom restriction on 
the inverse of hasPrecondition would be fine. Note that this means that 
the same "pre"condition could be used both as a precondition and as a 
"regular" test condition in the same composite process. If I had a 
conditional process:

	Pre: P
	If P then Q else R

Then, assuming P isn't significantly time sensitive, I can eliminate 
the redundant conditioanl test and branch, since the actual behavior of 
the above process will be the same as
	Pre: P
	Seq: Q

Bijan "Back from Travel" Parsia.
Received on Saturday, 8 November 2003 17:17:11 UTC

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