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Re: Blank Nodes and SPARQL

From: Kendall Clark <kendall@monkeyfist.com>
Date: Mon, 11 Jul 2005 14:25:59 -0400
To: Dan Connolly <connolly@w3.org>
Cc: DAWG Mailing List <public-rdf-dawg@w3.org>, Ron Alford <ronwalf@umd.edu>, "Seaborne, Andy" <andy.seaborne@hp.com>, "Eric Prud'hommeaux" <eric@w3.org>, public-rdf-dawg-comments@w3.org, Amy Alford <aloomis@glue.umd.edu>
Message-ID: <20050711182559.GA21969@monkeyfist.com>

On Mon, Jul 11, 2005 at 01:18:54PM -0500, Dan Connolly wrote:

> > Thinking about it a little more, it does seem to change the semantics of
> > every graph that gets rewritten in that way.
> 
> The _!:... mechanism has the same effect, no? In the context in
> which it's used, it works logically like a URI; i.e. it matches
> the way URIs match.

I don't believe so. As Ron says in another message, OWL DL says some things
(i.e. restrictions) have to be anonymous. _!:foo is still anonymous, while a
URI isn't.

So they may be, from some point of view, equivalent, but they have different
effects, one of which is unacceptable IMO.

> > 1. It make sense (which is a good thing)
> 
> I accept that as your position; I don't share it.

Care to say why you claim that it doesn't make sense? (I assume you don't
mean that making sense isn't a good thing! :>)

> This is more than syntactic sugar for something that can already
> be expressed, isn't it? 

Hmm, yeah, maybe "syntactic sugar" is the wrong way to put it. I guess I
meant to say that it's a syntactic solution, rather than sugar for something
else that can already be expressed.

> What is this short for?
> 
>   SELECT ?MBOX
>    WHERE { _!:l55c33 foaf:mbox ?MBOX. }.

Okay, so it's not sugar per se.

This is the first I've heard you say that one of Andy's solutions to the
bnode problem isn't a solution. I guess we disagree about that.

> > 4. It feels right -- i.e., it's sufficient to the problem, but not overly
> > powerful, such that other, hard-to-see issues might be raised.
> 
> Adding a new type of term (in addition to URI, literal, bnode, and
> universal variable) makes me quite nervous about hard-to-see issues.

Fair enough. Nervousness, like mileage, obviously varies.

Kendall Clark
Received on Monday, 11 July 2005 18:27:30 GMT

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