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RE: motivation for bNodes/existentials in RDF; note for parsers

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Thu, 04 Apr 2002 21:06:11 +0100
Message-Id: <5.1.0.14.2.20020404205958.0412c010@joy.songbird.com>
To: "Massimo Marchiori" <massimo@w3.org>
Cc: <w3c-rdfcore-wg@w3.org>
At 07:27 PM 4/4/02 +0200, Massimo Marchiori wrote:
>Anway, this is leading away from the other point of the discussion: the
>existential interpretation.
>Now, before we got lost here, just a note: no fundamental objections
>to the existential interpretation per se, as it's in the MT, and the MT
>is (citing the abstract) "a model-theoretic semantics for RDF and RDFS",
>(so, "a", not "the"). But, as this point has never well been clarified so
>far, if the "a" changes into a "the", then the level of criticisms
>radically changes, and that's where more severe stop-over criticisms can
>occur.

I don't think the indefinite article means that it's optional.  Rather, one 
could devise a different MT with the same entailment properties.  In my 
view, RDF developers MUST be able to depend on the semantics as set out by 
the MT.

>RDF Core was not chartered to normatively do these two, and not chartered to
>do the "web logic".
>There's nothing like a "variable" in RDF. The moment you put in variables,
>existential quantification, entailment, you're trying to do RDF logic,
>which is a different wg (and, a different spec than M&S).

The decision we took on the interpretation of blank nodes as existentially 
quantified was, in considerable part, based on statements of members of the 
original RDF group who are members of the current group that this was 
indeed the intent of the original RDF specification.  So it seems that 
_not_ to continue this, in absence of compelling reason, would be in 
violation of our charter.

>If MT is just a proposal, fine (even more: good! as, it helps to
>provide a possible good starting point for a next RDF Logic/Query wg).
>If on the other hand, it aims to define now the normative RDF Logic,
>then I think it's truly beyond scope.

In my view, this is absolutely not the case.  One of the very strongly 
expressed views informing the formation of the RDFcore group was 
uncertainties caused by the lack of any formal semantics.  We had a very 
clear message that this was something that needed to be fixed, and we've 
spent a lot of group energy doing so.

#g


-------------------
Graham Klyne
<GK@NineByNine.org>
Received on Thursday, 4 April 2002 15:04:32 EST

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