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Re: [UCR] RIF needs different reasoning methods

From: Francois Bry <bry@ifi.lmu.de>
Date: Wed, 08 Mar 2006 15:02:29 +0100
Message-ID: <440EE3F5.2090803@ifi.lmu.de>
To: Bijan Parsia <bparsia@isr.umd.edu>
CC: public-rif-wg@w3.org

Bijan Parsia wrote:
> Part of my confusion is that, in that email, it seemed as if these
> rules were all semantically equivalent...i.e., that the ONLY
> distinguishing factor was the proof theory employed (and that all the
> proof theories were supposed to be sound and complete for those
> semantics).
The sentence in parentrheses does not seem to be right.
> If the only motivation (from observable behavior) is performance
> (another thing I gleaned from your email), then why *is* it important
> to specify the *method* rather than just specify an engine
> known-to-be-fast-for-my-ruleset?
Mewthods are more abstrract and give rise to more portability. If I teel
you, "this trip can be made in 2 hours on a bike", I am giving you a
more convenient information than "this trip can be made in 2 hours on my
Peugeot 2X755". You see what I mean?
> One possibility I thought of is that, e.g., in several systems (JESS
> and Jena, for example), you can indicate that some rules are to be
> evaluated using the backward chainer, rather than a forward chainer.
> Presumably, if one is sticking to the declarative bit, it makes no
> difference to the semantics, but can have a dramatic effect on
> performance. 
In many cases, such a difference would decide about ternmination and
non-termination.

> Now this is a totally different reason, afaict. In fact, it almost
> sounds like a *marketing* (or pragmatics) point. 
It is a pragmatic point. Applied research and W3C standards are about
pragmatics.
> If they *are* subtantive, then I need a example where the rules 1)
> have the same (declarative?) semantics, 2) have an behavioral
> difference depending on whether they are marked as one kind of rule
> rather than another, and 3) have a *further* behavioral difference
> (other than performance) based on the specified (sound and complete)
> proof theory.
I tried to give such an example in my message. Maybe could we look at it
opnce again?

Regards,.

François
Received on Wednesday, 8 March 2006 14:02:34 GMT

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