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

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Mon, 25 Mar 2002 17:47:24 +0000
Message-Id: <>
To: "Massimo Marchiori" <massimo@w3.org>
Cc: "Dan Connolly" <connolly@w3.org>, "Pat Hayes" <phayes@ai.uwf.edu>, <w3c-rdfcore-wg@w3.org>, "Lynn AndreaStein" <las@olin.edu>

The discussion of whether or not to use Skolemization did come up, at some 
length as I recall, in our first F2F.  The conclusion is reflected 
(briefly) in the current MT document:


In particular:
Also, skolemization would not be an appropriate operation when applied to 
anything other than the antecendent of an entailment. A skolemization of a 
query would represent a completely different query.

[Pat:  I think there's a typo there 'antecendent'->'antecedent']


At 02:10 PM 3/25/02 +0100, Massimo Marchiori wrote:

> > -----Original Message-----
> > From: Dan Connolly [mailto:connolly@w3.org]
> > Sent: Saturday, March 23, 2002 3:59 AM
> > To: Pat Hayes
> > Cc: w3c-rdfcore-wg@w3.org; Massimo Marchiori; Lynn AndreaStein
> > Subject: motivation for bNodes/existentials in RDF; note for parsers
> >
> >
> > Pat, Dave,
> >
> > I just explained to another colleague of
> > mine, Massimo, that RDF formulas are not
> > just sets of ground facts...
> >   (and
> >     (p1 s1 o1)
> >     (p2 s2 "lit2")
> >     ...
> >    )
> >
> > but that RDF can express existential quantification...
> >
> >  (exists (?b1 ?b2 ?b3 ...)
> >   (and
> >     (p1 s1 ?b1)
> >     (p2 ?b2 "lit2")
> >     ...
> >    )
>In these kind of sentences I always have to argue with Dan, as
>he always says so and I always reply in the usual way...
>So, restating the above, the *current version of the
>RDF Model theory* states that the interpretation of RDF
>ought to be ... bla.
>This is important to remember, as it's a fundamental design choice
>that it's going to be decided, but it's not present in the
>"normative RDF" (M&S) document.
> > Have you added some explanation about that
> > to the model theory spec?
>I think what concerns me most, in this context, is the appropriate
>explanation of why this is the choice to make, versus the most
>obvious choice we have at our disposal (i.e., skolemization).
>That is, what are the pro's and con's that favour the existential
>approach vs the skolem one?
>AFAIK the second one has been so far the natural choice (the
>"understood standard" if you want ;), for some good reasons.
>So, summing up, since this is a fundamental architectural decision
>(not just syntactic sugaring) concerning RDF, what is most interesting
>is to give the reasons for this interpretation vs the easiest skolem one.
>Yes, it's a classic "last call" fundamental question, because that spawns
>into the data model, on which there are many things to discuss, but well,
>Dan brought the matter up early ;)
>ps Apologies if the pro-con analysis and motivation has already been posted,
>if so I probably missed it (not an unlikely possibility).

Graham Klyne
Received on Monday, 25 March 2002 13:13:23 UTC

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