On Jul 2, 2010, at 11:06 AM, Paul Gearon wrote:
On Fri, Jul 2, 2010 at 8:34 AM, Pat Hayes <pha...@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
