W3C home > Mailing lists > Public > semantic-web@w3.org > July 2010

Re: Subjects as Literals

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 2 Jul 2010 10:34:44 -0500
Cc: Reto Bachmann-Gmuer <reto.bachmann@trialox.org>, Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-Id: <D8342A85-5E7A-4C38-9703-07BED1E291B4@ihmc.us>
To: Paul Gearon <gearon@ieee.org>

On Jul 2, 2010, at 7:27 AM, Paul Gearon wrote:

> On Fri, Jul 2, 2010 at 2:16 AM, Reto Bachmann-Gmuer
> <reto.bachmann@trialox.org> wrote:
>> Serialization formats could support
>>
>> "Jo" :nameOf :Jo
>>
>> as a shortcut for
>>
>> [ owl:sameAs "Jo"; :nameOf :Jo]
>>
>> and a store could (internally) store the latter as
>>
>> "Jo" :nameOf :Jo
>>
>> for compactness and efficiency.
>
> While this may be possible, you've promoted owl:sameAs to have a true
> semantic relationship at this level. You're treating it as if it
> really does mean "equals".

Well, it does mean that, according to the OWL specs.

> Given your scenario, I'd expect:
>
> [ owl:sameAs "foo", "bar" ]
>
> to lead to the following being stored:
>
> "foo" owl:sameAs "bar"
>
> Since we only got here because owl:sameAs is being treated as having
> equality semantics at the RDF level, then I *think* that this is
> inconsistent.

Yes, it is.

> I'll confess that I don't understand some of the
> subtleties surrounding datatypes

You didn't use datatypes in that triple, so...

> , so I'll let others confirm this for
> me. Presuming that it *is* wrong, then this introduces the possibility
> of inconsistent RDF, something that is currently impossible (with the
> exception of XML literals, but that's another story)

Actually its the same story. Literals generally have *fixed*  
interpretations, fixed by the semantics of the language. Whenever you  
have this, you have the possibility of inconsistencies.

> , and something we
> don't want. I'm more than happy for inconsistencies to be possible at
> a higher level (e.g. OWL-DL), but not in RDF.

Why not? Inconsistency is just another way to say entailments. If  
there are no inconsistencies possible in RDF, then there are no  
significant entailments from any RDF. So RDF is just a bunch of  
triples, with nothing that can be done to them except look at them.

Pat


>
> Even if I'm wrong and it's OK, I'd still feel uncomfortable building a
> system that can do this.
>
> Regards,
> Paul Gearon
>
>

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Received on Friday, 2 July 2010 15:35:51 UTC

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