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Re: Patel-Schneider Paradox ...

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 15 Feb 2002 16:50:02 -0500
To: phayes@ai.uwf.edu
Cc: danbri@w3.org, www-webont-wg@w3.org
Message-Id: <20020215165002G.pfps@research.bell-labs.com>
From: Pat Hayes <phayes@ai.uwf.edu>
Subject: Re: Patel-Schneider Paradox ...
Date: Fri, 15 Feb 2002 02:27:33 -0500

> >From: Dan Brickley <danbri@w3.org>
> >Subject: Re: Patel-Schneider Paradox ...
> >Date: Fri, 18 Jan 2002 17:00:34 -0500 (EST)
> >
> >>  RDF 1.0 was
> >>  kept pretty simple, and it isn't suprising that we're pushing at the
> >>  limits of what we can get done with such a simple representational system.
> >
> >>  Dan
> >
> >
> >I just cannot let this statement go by without registering the strongest
> >protest.
> >
> >I believe that RDF is *not* simple.  On the contrary, I firmly hold the
> >view that RDF is one of the most complex representation formalisms I have
> >ever encountered.
> >
> >Complexity is not (solely) measured by the amount of implementation effort
> >required to build a minimal parser for a language, although even building a
> >minimal parser for RDF is considerably more complex than building a minimal
> >parser for many representation formalisms.  Complexity also has to do with how
> >hard it is to understand the syntax of a representation formalism, how hard
> >it is to come up with an understanding of the basic principles of the
> >representation formalism, and how hard it is to determine just what the
> >constructs of the representation formalism mean, among other aspects.  In
> >all three of the above areas RDF is significantly more complex than most
> >representation formalisms.
> >
> Well, I can't let that go by, either. (Let me see, how to phrase 
> this....) Balls.
> RDF is about as simple as a representational language could possibly 
> be. It is first-order positive existential conjunctive logic 
> restricted to binary relations. Period. (Oh, well, it also has 
> datatyping for literals, but that isn't very complicated either.)
> There is nothing complex or difficult about it. It is easy to map it 
> into a conventional logical notation, and trivial to map it into KIF. 
> Its entire proof theory can be captured in one lemma (see the MT 
> document) and its model theory can be written on a postcard. Parsing 
> the graph syntax can be done by a finite-state machine in one pass. 
> If you can see any complexity in it, Peter, you must be smoking some 
> really good ganja.
> Pat Hayes

If your statements above are true, then what is the RDF Core WG doing?

You and I may both agree that the understandable parts of the formal
meaning of RDF is dead trivial.  However, there is lots more to RDF than
that.  For example,

1/ RDF reification - particularly as understood / used
2/ RDF containers - particularly alternative, but even sequences are complicated
3/ RDF syntax - particularly some of the automatic reification components

To add to the above RDF M&S is vague, unclear, misleading, and
self-contradictory, even in the ``formal'' parts, which only adds to the
complexity of RDF. 

Then we get to RDFS, which has its own complexity, including

1/ two readings for constraints, neither well-specified
2/ the conditions on domain and range
3/ properties with no formal meaning
4/ the extensibility mechanism

Now the RDF Core WG is trying very hard to address some of these sources of
complexity, but the end result, as far as I can see, is *not* going to be a
simple formalism.

So, I still maintain that RDF is an extremely complex representation
formalism, as is RDFS.  (Well maybe it would have been better to say that
RDF is an extremely complex specification, but I still say that RDF is an
extremely complex representation formalism.)

Peter F. Patel-Schneider
Bell Labs Research
Received on Friday, 15 February 2002 16:51:46 UTC

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