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Re: Subjects as Literals

From: Hugh Glaser <hg@ecs.soton.ac.uk>
Date: Wed, 30 Jun 2010 20:40:55 +0000
To: David Booth <david@dbooth.org>, Kingsley Idehen <kidehen@openlinksw.com>
CC: "nathan@webr3.org" <nathan@webr3.org>, Pat Hayes <phayes@ihmc.us>, Toby Inkster <tai@g5n.co.uk>, Dan Brickley <danbri@danbri.org>, Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-ID: <EMEW3|ca6dd6bb50809d118948a9947aaf3018m5YLfJ02hg|ecs.soton.ac.uk|C8516A67.15724%hg@ecs.soton.ac.uk>

On 30/06/2010 19:55, "David Booth" <david@dbooth.org> wrote:

> On Wed, 2010-06-30 at 14:30 -0400, Kingsley Idehen wrote:
>> Nathan wrote:
>>> Pat Hayes wrote:
> [ . . . ]
>>> Surely all of the subjects as literals arguments can be countered with
>>> 'walk round it', and further good practise could be aided by a few
>>> simple notes on best practise for linked data etc.
>> 
>> IMHO an emphatic NO.
>> 
>> RDF is about constructing structured descriptions where "Subjects" have
>> Identifiers in the form of Name References (which may or many resolve to
>> Structured Representations of Referents carried or borne by Descriptor
>> Docs/Resources). An "Identifier" != Literal.
>> 
>> If you are in a situation where you can't or don't want to mint an HTTP
>> based Name, simply use a URN, it does the job.
> 
> Can you explain *why* you think literals should not be permitted as
> subjects?  The rationale you have given above sounds like it is saying
> that literals should not be subjects because RDF does not permit
> literals to be subjects.
> 
> IMHO, RDF should allow "anyone to say anything about anything" -- not
> "anyone to say anything about anything . . . except a literal".
Actually, I think it is even worse than that.
RDF permits anyone to say anything about anything . . . except a literal if
it is the subject of the property you want to use for the description.

So I can say: foo:booth isNamed "David Booth"
But of course I can't say: "David Booth" isNameOf foo:booth

Now how bizarre is that?

Mind you, I have sometimes wondered what happens if I try to assert
something like

<owl:ObjectProperty rdf:ID="isNamed">
  <owl:inverseOf rdf:resource="#isNameOf"/>
</owl:ObjectProperty>

I guess I do not understand owl:inverseOf or that some type constraint is
violated or maybe it's a RDF/OWL Full/OWL Lite issue?

I also have a sense that there may be some confusion about the implications.
Using a string as a subject does not imply that the string is an identifier
any more than using it as an object.

Of course (pace Jeremy), I don't necessarily agree that there should be any
changes - we do not have sufficient Semantic Web take up that we can think
of changing things without a serious discussion of costs and implications.
We have gone a long way down this road managing without.

Cheers
Hugh

> However, if you see some specific harm in permitting statements about
> literals, please tell us what that harm would be.
> 
> 
Received on Wednesday, 30 June 2010 20:43:17 UTC

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