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Re: Where are the semantics in the semantic Web?

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Fri, 25 Nov 2005 13:53:09 -0500
Message-Id: <f7594ceb896f886b9edeed33ffc54f4a@isr.umd.edu>
Cc: jeff@inf.ed.ac.uk, public-sws-ig@w3.org
To: Harry Halpin <hhalpin@ibiblio.org>

Can I just say that I'm a snarky mood and this thread really pushes my  
snark buttons. I've been trying to edit it out, but some slips through.

On Nov 25, 2005, at 1:28 PM, Harry Halpin wrote:

> Bijan,
> There's a difference between formal semantics as used in denotational
> semantics and the operational semantics ala XQuery/XPath.

I believe that *is* a denotational semantics, in the sense of:
	http://citeseer.ist.psu.edu/context/8571/0

But perhaps I'm wrong.

> XQuery/XPath
> has formal semantics for type-checking using XML Schema types.

Is it operational?

> That's
> *what it does*,

*Yes indeed*. (<--I'm not sure about this, but given the extra  
emphasis, I thought I should reply in kind ;))

> and it does well. It in no way provides a uniform formal
> semantics for any given XML document.

Most surely it does, in the sense that it provides a typing for it  
(that is, a mapping into a model).

> After all, I can code up FOL or
> anything else in XML

Not in XML or XML Schema alone, I'll bet. Well, I'm not sure about the  
latter, but imagine you stick to a decidable fragment of XML Schema,  
then for sure not.

> and the operational semantics of XQuery tell me
> *nothing* about its operations qua FOL.

But this is, well, a lame argument. You're saying that XML's formal  
semantics isn't expressive enough to formalize FOL. Well, uh, yes. So  
too for RDF and OWL.

>  However, RDF does provide a
> uniform formal semantics (although not too interesting!) for any given
> RDF statement. Now, one can code FOL in RDF, and RDF will tell you
> things about those FOL statements, but it will be using the RDF model.

Sorry, I think you are seriously confused. I totally fail to see that  
XML is *qualitatively* worse off. It has a formal semantics which show  
it (well, this isn't clear, but lets assume) insufficient to formalize  
FOL. So? So too for RDF.

Since various schema languages are expressive enough to encode 3sat, I  
think you might be surprised at what they can, in fact, say:
	http://www.idealliance.org/papers/extreme03/html/2003/Lyons01/ 
EML2003Lyons01.html
	http://lists.xml.org/archives/xml-dev/200304/msg00148.html

So, if you coded your propositional logic properly, you'd even get the  
right semantics!

> What of course we want is to code FOL and get results via the FOL  
> model,
> but at least with
> RDF we have something rather than nothing.

We have a something that is probably worse than nothing. The other  
something might be worse than nothing too, but it's not nothing.

Cheers,
Bijan.
Received on Friday, 25 November 2005 18:53:35 GMT

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