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Re: RDF Query -- possible WG charter draft for discussion

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Mon, 10 Nov 2003 19:39:31 -0500 (EST)
Message-Id: <200311110039.hAB0dVw13786@pantheon-po01.its.yale.edu>
To: danbri@w3.org
Cc: www-rdf-rules@w3.org, eric@w3.org, em@w3.org, sandro@w3.org, massimo@w3.org, connolly@w3.org


Comments on the draft "Rules" charter:

Comment 1: I realize that this question may be raising a dead issue, but why is
everyone so focused on rules, and not "propositions"?  

The draft charter says

  The need for rules of the form "for all X, Y, and Z, if P(X,Y,Z) then
  Q(X, Y, Z)" is clear.

But the quoted statement is not considered a rule at all by
logicians.

I know this is to some extent a matter of notation.  One can argue
that a Prolog-style rule such as

     q(X,Y,Z) :- p(X,Y,Z)

is just a notational variant of the version above with neutral
directionality and explicit quantifiers.  But what makes it a good
notational variant?  Presumably the fact that there is a particular
inference algorithm that uses it.  So does the charter imply that
certain inference algorithms (or their specifications) will be made
into standards?

The Prolog rule is not a good way of representing the quantified
statement if it's going to be embedded into contexts such as "None of
the companies in the list ... is responsible for the fact that for
all X,Y,Z ...."  


Comment 2: What does the charter mean when it says that the OWL Rules
proposal "does not maintain independence between Rules and OWL"?  Is
that good or bad?  I assume the issue is brought up earlier in the
charter, but I can't find it.


Comment 3: The section on "Syntax" jumbles up two questions: What does
the syntax look like in RDF?, and what does the resulting RDF look
like when put into XML?  Aren't these orthogonal?

The various possible syntaxes are describe in vague terms
that only insiders can decipher.  E.g.:

  Extension of RDF/XML. An XML syntax could be developed which extends
  RDF/XML by adding a rule construct and scoped, quantified variables,
  but otherwise maintains compatibility. The downsides here are
  verbosity, plus carrying forward all the existing issues with RDF/XML
  as a syntax. This group is expected to consider this as one possible
  XML syntax.

Isn't this what CWM/N3 does?  I don't think of it as verbose.

I have a feeling I'm missing the meaning here entirely.  If you have
an XML rule syntax that "maintains compatibility," you have to
introduce the long-desired idea of marking parts of rules as "not
asserted merely because they're explicit."  Is that what the quoted
paragraph means?  If not, what does it mean?  

_What_ existing issues with RDF/XML syntax?  Aren't they going to be
"carried forward" no matter what the Rules group does?

What does the Non-XML option come down to?  How can there possibly be
a language on the SW that doesn't have an XML serialization?  

-- 
                                   -- Drew McDermott
                                      Yale Computer Science Department
Received on Monday, 10 November 2003 19:39:34 GMT

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