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 12:28:00 -0500
Cc: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-Id: <F10B91B5-144E-4E87-B540-643F4BF9A5CC@ihmc.us>
To: Paul Gearon <gearon@ieee.org>

On Jul 2, 2010, at 11:06 AM, Paul Gearon wrote:

> 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.

Close, but I wouldn't say that RDF is meaningless exactly. Its  
semantics is minimal, but it does give it some meaning. Its the just- 
the-basic-facts-Ma'am part of logic: no conditionals, no quantifier  
scopes, and most importantly of all, no negation. Which is why it is  
contradiction-free.

It wouldn't take very much to make into full first-order logic: all it  
needs is a scoping mechanism (think graph literals in N3 or named  
graphs, or my 'surfaces' idea from the Blogic talk) and negation. Mind  
you, that scoping mechanism would drive a truck through triple-store- 
based implementations, I suspect. Back to tree structures and  
Sexpressions, no doubt :-)

Pat

>
> Regards,
> Paul Gearon
>
>

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Friday, 2 July 2010 17:29:00 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 1 March 2016 07:42:21 UTC