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RIF (was Re: [ontolog-forum] Current Semantic Web Layer Cake)

From: Sandro Hawke <sandro@w3.org>
Date: Tue, 31 Jul 2007 15:12:00 -0400
To: "John F. Sowa" <sowa@bestweb.net>
Cc: Valentin Zacharias <Zacharias@fzi.de>, phayes@ihmc.us, ivan@w3.org, juanfederico@gmail.com, semantic-web@w3.org
Message-ID: <18631.1185909120@ubuhebe>


"John F. Sowa" <sowa@bestweb.net> writes:
> 
> Valentin,
> 
> The semantic foundation for RDF and OWL is consistent with the
> model-theoretic foundation for Common Logic.  Any rule language
> that is consistent with RDF and OWL must be consistent with
> that same model-theoretic foundation.
> 
> VZ> In their own words [1]: "A dialect is a rule language with
>  > a well-defined syntax and semantics. This semantics must be
>  > model-theoretic, proof-theoretic, or operational in this order
>  > of preference."
>  >
>  > [1]: http://www.w3.org/TR/rif-core/
> 
> That is not a coherent definition.  What it implies is that the
> rules have no consistent semantics.

If I could jump in here, I think I can clarify the situation.

RIF is not a rule language; it a family of related rule languages.
We're calling each RIF language a RIF "dialect".  Our plan is to
encourage the dialects to use the same syntax when the semantics line
up, and to require the same semantics whenever the same syntax is
actually used.  This should allow RIF to appear to users as being
essentially one language -- they use the syntactic elements they want,
and get the associated semantics, without paying attention to dialects
-- but formally the semantics are to be specified at the dialect level.
(It's just a hypothesis that users will benefit from being able to mix
dialects.  Hopefully it wont be too hard to allow it, and there wont be
any great cost to users.)

The sentence quoted above -- about the different types of semantics --
is speaking to dialect designers (perhaps not very clearly).  The idea
is that when you're designing a dialect, you should specify the
semantics using Model Theory.  If you can't do that, then you should use
Proof Theory.  If you still can't then you may fall back to an
operational definition.  This is necessary, as far as we can tell,
because we don't have Model-Theoretic or Proof-Theoretic approach to
defined the semantics of the Production Rule systems which dominate the
Business Rules market.

> VZ> Which also is probably the reason for the "misplacement" of
>  > the unified logic box - there is no (known) unifying logic for
>  > the union of these formalisms.
> 
> If they allow that loophole, they destroy any chance of
> interoperability.  Why on earth would anyone define a
> "Rule Interchange Format" that allows different systems
> to interpret the rules in inconsistent ways?
> 
> There is a simple solution to this problem:  Send the RIF
> committee back to the drawing board until they agree to
> a coherent definition.  If they can't agree, then just say
> that RIF is deprecated for use in systems that are required
> to be interoperable.

The RIF Working Group had a broad mission to cover both logical rule
languages and non-logical rule languages (like the Business Rules
systems mentioned above).  One part of our work, focussed on logical
dialects (starting with a "Basic Logic Dialect") is firmly based on
Model Theory, and should be well aligned with RDF and the Semantic Web.

If we consider the "RIF" box in the layer cake to be "RIF BLD" then I
think we're in good shape with the Unifying Logic.  If we do this, the
concerns raised above -- the loophole, etc -- don't come into play.

See also a recent announcement by the chairs:
http://www.w3.org/blog/SW/2007/07/20/rif_wg_agrees_to_basic_logic_and_pr_dial

   -- Sandro   (RIF-WG W3C Staff Contact)
Received on Tuesday, 31 July 2007 19:13:37 UTC

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