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RE: Question about literals in subject position

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 28 Sep 2009 14:47:26 +0000
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>, "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693EA8D533@GVW1118EXC.americas.hpqcorp.net>

> -----Original Message-----
> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg-
> request@w3.org] On Behalf Of Birte Glimm
> Sent: 28 September 2009 14:50
> To: public-rdf-dawg@w3.org Group
> Subject: Re: Question about literals in subject position
> [snip]
> > We could change the definition to allow literals as subjects - in order
> to maintain compatibility absolutely with the Query 1.0 spec, the
> restriction could be moved into the definition of simple entailment
> matching, freeing it up for other entailment regimes.
> >
> > Query 1.0 notes that the RDF WG knew of no reason not permit them except
> the syntax issues with RDF/XML.
> I am not advocating that literals in subject positions should be
> allowed. If they are allowed, however, they are another source of
> infinite answers under at least RDF(S) entailment regimes and we have
> to have conditions in space to prevent infinite answers from this
> source. The restriction that I have proposed would work for literals
> in subject position, but we have discussions at the moment about we
> should just restrict the use of rdf:_1, rdf:_2, ... which are the only
> real source of infinite answers at the moment.

We should plan for literals in subject positions if at all possible, that is, my ideal is finding a reason why not - yes, we need to limit the solutions in someway to avoid the infinite. 
It seems like some systems already some processing with it (e.g. Paul's message where the results are limited to the terms used in the base graph) and it may well happen in the future.  The current spec tries to be open to the possibility.

(If we find there is a major roadblock, then that will be useful input to future proposal to RDF.)


Received on Monday, 28 September 2009 14:48:53 UTC

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