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Re: Subjects as Literals

From: Paul Gearon <gearon@ieee.org>
Date: Fri, 2 Jul 2010 09:06:05 -0700
Message-ID: <AANLkTimaD7qfHsa3bQ_M7aj_ajKI9oJgv4sWSKl-UtF0@mail.gmail.com>
To: Pat Hayes <phayes@ihmc.us>
Cc: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
On Fri, Jul 2, 2010 at 8:34 AM, Pat Hayes <phayes@ihmc.us> wrote:
>
> On Jul 2, 2010, at 7:27 AM, Paul Gearon wrote:
>
>> 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.

Of course. My point here was that it's a semantics that it being
applied at the RDF level.

>> 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...

I misspoke (mis-typed?). I was thinking of the value space. I tend to
lump untyped literals in with the typed ones, even though I know
they're not the same. (sloppy thinking leading to sloppy language)

>> , 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.

Well that's my point. Isn't that was RDF is? If not, then I withdraw
my objection.

I was under the impression that entailments could only appear when we
provide semantics to a vocabulary, such as RDFS. Without that, RDF is
just a bunch of triples that lets us build meaningless structures. We
can apply meaning to these structures through our vocabularies, but
that's our choice, and not something inherent in RDF.

Well, that's how I understand it. Now that I've said it, I'm curious
to know how close to the intended "truth" this interpretation lies.

Regards,
Paul Gearon
Received on Friday, 2 July 2010 16:06:39 UTC

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