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RE: Questions about Update 1.1

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Sun, 18 Oct 2009 14:04:53 +0000
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>, Steve Harris <steve.harris@garlik.com>
CC: "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693FA225DA@GVW1118EXC.americas.hpqcorp.net>


> -----Original Message-----
> From: b.glimm@googlemail.com [mailto:b.glimm@googlemail.com] On Behalf Of
> Birte Glimm
> Sent: 16 October 2009 16:15
> To: Steve Harris
> Cc: Seaborne, Andy; public-rdf-dawg@w3.org Group
> Subject: Re: Questions about Update 1.1
> 
> [snip]
> >>> 2) Can you delete bNodes with DATA? DELETE DATA { <a> <b> _:z }
> >>> doesn't really make much sense. Some stores (including Jena and
> >>> 4store) allow you to quote bNodes like DELETE DATA { <a> <b> <_:z> }
> >>> but that's non-standard.
> >>
> >> Yes - this is more of a problem now we have update and not just query.
> >>
> >> We could document the <_:...> usage.
> >
> > Garlik would be in favour of that. We've found it invaluable when dealing
> > with FOAF data in particular.
> > However, I'm not quite sure how it fits in with the semantics of RDF. It's
> a
> > form of skolemisation I suppose, in our case it just externalises what's
> > happening inside the store.
> 
> Hm, it could be quite difficult for users to know what the actual
> bnode IDs are because you might have to rename them in a merge. If I
> think ahead to OWL where you have imports, we just name them all apart
> in any case, so if a user asks our OWL reasoner to load some ontology
> that contains <a> <b> _:z, it will end up as <a> <b> _:genID_1 in the
> reasoner. 

The <_:...> syntax would have to refer to the internal generate symbol (genID_1), not the synatx used in the file -- after all, if you read the same file twice, you will get different bNodes.

It's for addressing some that references the internal identifier (genID_1) so it might look like 
<_:genID_1> or <_:f3ab9c0e-293d-11b2-801e-a9ebf2123a5c>

This also means you have to be able to get the internal identifier in the first place.

	Andy

> Now the user would first have to query and hope that the
> query reveals the internal bnode name and then it can be deleted.
> It does not really speak against the usage of <_:z> it would just be
> hard to use with systems that freely rename bnodes, which is perfectly
> ok for a system to do. So I am not totally against it, but it might
> cause confusion for users because the system behavior is hard to
> predict.
> 
> Birte
> 
> > - Steve
> >
> >
> 
> 
> 
> --
> Dr. Birte Glimm, Room 306
> Computing Laboratory
> Parks Road
> Oxford
> OX1 3QD
> United Kingdom
> +44 (0)1865 283529
Received on Sunday, 18 October 2009 14:06:17 GMT

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