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Re: Blank Nodes and SPARQL

From: Dan Connolly <connolly@w3.org>
Date: Mon, 11 Jul 2005 13:18:54 -0500
To: kendall@monkeyfist.com
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: <1121105935.10719.250.camel@localhost>

On Mon, 2005-07-11 at 12:52 -0400, Kendall Clark wrote:
> On Mon, Jul 11, 2005 at 11:33:59AM -0500, Dan Connolly wrote:
> > 
> > On Sun, 2005-07-10 at 22:04 -0400, Ron Alford wrote:
> > > After consulting with the lab, we have decided that the namespace
> > > splitting proposal (_!:...) is the best way to deal with the use cases
> > > that have been brought up.
> > >
> > > While we believe that the protocol prebinding is nice and generally
> > > useful, we would prefer a syntax level solution to the bnode problem.
> > > 
> > > The function extension (ext:bnodelabel) comes in a distant third.  It
> > > adds annoying overhead to templating queries.  We were also concerned
> > > with how well implementations will deal with function extensions.
> > 
> > And what of the "Dynamically assign identifiers" option? I'm
> > interested to know whether you find it acceptable.
> 
> I probably shouldn't answer for Ron, here, but I asked our OWL DL friends,
> and they didn't like this at all.
> 
> 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.

> As Ron said, we strongly prefer the "split the bnode label space" solution
> that Andy pointed out. Here's why:
> 
> 1. It make sense (which is a good thing)

I accept that as your position; I don't share it.

> 2. It reflects actual practice (people seem to be doing this on their own)

True.

> 3. It's a relatively simple spec change, needing only some description of
> the actual syntactic sugar (so that everyone does the same thing)... How
> Andy chooses to do this -- we discussed just setting a convention or making
> a new grammar production -- is something we're comfortable leaving to his
> judgment.

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

  SELECT ?MBOX
   WHERE { _!:l55c33 foaf:mbox ?MBOX. }.


> 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.

> Hope this helps elucidate our position a bit.
> 
> Kendall Clark
> 
> PS--I'm cc'ing the DAWG list.
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Monday, 11 July 2005 18:18:59 GMT

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