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Re: Owl Rules and RDF Semantics

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 10 Nov 2003 14:21:57 -0500 (EST)
Message-Id: <20031110.142157.42991283.pfps@research.bell-labs.com>
To: drew.mcdermott@yale.edu
Cc: www-rdf-interest@w3.org, www-rdf-logic@w3.org

From: Drew McDermott <drew.mcdermott@yale.edu>
Subject: Re: Owl Rules and RDF Semantics
Date: Thu, 6 Nov 2003 17:18:02 -0500 (EST)

[...]

> What I would like to see is
> a more consistent and open-ended approach to formal languages on the
> semantic web.  In particular:
> 
> > The mechanism for encoding languages in RDF should be independent of
>   any particular language.  There are two basic requirements for
>   encoding a language in RDF: Make sure the triples in the encoded
>   version don't actually say anything in the domain being encoded; and
>   figure out a way to handle bound (or free) variables.  There are
>   several proposals on the table (I should mention the RDF encoding of
>   RuleML).  It would clarify things if W3C would endorse a standard.
>   It would be easier to compare languages without being distracted by
>   the details of encodings.

Hmm.  I'm not too sure about this.  What is the cost of having different
kinds of encodings for different languages?  I don't think that it is very
high.

> > It should be acknowledged that encoding a language is an exercise in
>   _syntax_.  Somehow the idea of the "semantic" web has got people to
>   shun syntax as something obsolete or unclean.  They are willing to
>   produce a formal syntax for their language, but only as a dirty
>   chore to be cleared away before getting to the semantics.  That
>   means we see paper after paper that encodes language after language
>   in RDF in slightly different ways, where the titles of the papers
>   emphasize the difference in semantics or inferential power between
>   their language and someone else's.  The poor reader gets to see lots
>   of angle brackets and some mumbling about the RDF model theory.
>   These papers would be a lot clearer if they used a concise surface
>   syntax, and then mentioned the W3C standard for embedding languages
>   in RDF, with a few words about how their syntax can be encoded using
>   the standard.  If this were done, the existence of a model
>   theory for RDF would be in most cases automatically irrelevant,
>   because the standard would have already established that the
>   universe of formulas has a formal description in RDF.

I agree that not worrying about how to encode a logical language in RDF
triples would result in much better papers about Semantic Web languages.

I'm not sure that this is the solution however.  I would instead say that
the adherence to RDF as the syntax for the Semantic Web is a serious
hindrance to its widespeard adoption.  (I have tried to play with the rules
as they have been laid down by W3C, and have found them very constraining
and time-wasting.)  

Why bother to even have an encoding of a Semantic Web language in RDF if
the only benefit is some partial syntactic compatability?  I don't find
anything wrong with having different syntaxes for different Semantic Web
languages.  In fact, I think that it is an excellent idea!  How much time
does it take to write a decent parser for a simple language (and logics
tend to have quite simple languages)?  It takes me less than one day to
write a parser for a logical language (admittedly one with little error
correction).

I might even go so far as to say that it would be a good idea to even step
outside of XML, but this would be even more heretical.

[...]

Peter F. Patel-Schneider
Bell Labs Research
Received on Monday, 10 November 2003 14:22:08 GMT

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