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RE: Question about literals in subject position

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Wed, 30 Sep 2009 18:53:18 +0000
To: Paul Gearon <gearon@ieee.org>
CC: "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA3693EA8DF36@GVW1118EXC.americas.hpqcorp.net>

> -----Original Message-----
> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg-request@w3.org]
> On Behalf Of Paul Gearon
> Sent: 29 September 2009 14:50
> To: Ivan Herman
> Cc: Birte Glimm; public-rdf-dawg@w3.org Group
> Subject: Re: Question about literals in subject position
> On Tue, Sep 29, 2009 at 3:47 AM, Ivan Herman <ivan@w3.org> wrote:
> >
> > Paul Gearon wrote:
> >> On Mon, Sep 28, 2009 at 9:49 AM, Birte Glimm
> >> <birte.glimm@comlab.ox.ac.uk> wrote:
> >>> [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 can't recall where I saw this, but didn't the RDF folks consider
> >> adding them in if a new version of RDF ever happens?
> >
> > This is certainly one of the issues that a new RDF group would have to
> > look at.
> >
> > _However_, and obviously putting the SemWeb Activity Head's hat on, it
> > is not clear at all in my mind that re-opening an RDF group would be a
> > good thing. RDF is at the centre of Semantic Web technologies, and
> > reopening the group _may_ send out a message of instability that the
> > market does not need. After all, it is only recently that we see this
> > market to become more stabilized and prospering. (And, yes, I am torn on
> > this issue and I know there will be disagreement on this...)
> >
> > We certainly should not expect any change on this subject during the
> > lifetime of this group.
> While I see the benefits of updating some aspects of RDF, I'm in
> complete agreement with your position here. I was speaking more to the
> mindset of the RDF designers, in that literal subjects aren't
> completely evil and that they may even be considered useful in some
> contexts.
> Thinking this way is why I suggest that SPARQL need not make any
> notion of literal subjects completely illegal. If they're allowed,
> then they work perfectly with RDF as it stands. Even if allowing
> literal subjects (especially through variable bindings) disagrees with
> SPARQL 1.0, I don't believe it does so in a way that would impact any
> existing systems. Indeed, some systems explicitly ignore the spec in
> this regard.

In SPARQL Query 1.0, literals subjects are just fine.

Definition: Triple Pattern

A triple pattern is member of the set:
(RDF-T union V) x (I union V) x (RDF-T union V)

"[The RDF core Working Group] noted that it is aware of no reason why literals should not
  be subjects and a future WG with a less restrictive charter may
  extend the syntaxes to allow literals as the subjects of statements."

It's the graph data that introduces the restriction.


> Paul

Received on Wednesday, 30 September 2009 18:54:23 UTC

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