On Jul 6, 2010, at 9:34 AM, Jiří Procházka wrote:
On 07/06/2010 03:35 PM, Toby Inkster wrote:
On Tue, 6 Jul 2010 14:03:19 +0200
"Michael Schneider" <schn...@fzi.de> wrote:
So, if
:s "lit" :o .
must not have a semantic meaning, what about
"lit" rdf:type rdf:Property .
? As, according to what you say above, you are willing to allow for
literals in subject position, this triple is fine for you
syntactically. But what about its meaning? Would this also be
officially defined to have no meaning?
It would have a meaning. It would just be a false statement. The
same as the following is a false statement:
foaf:Person a rdf:Property .
Why do you think so?
I believe it is valid RDF and even valid under RDFS semantic
extension.
Maybe OWL says something about disjointness of RDF properties and
classes
URI can be many things.
I think there are issues about RDF extensibility which haven't been
solved and they concern:
a) semantics
b) serializations
In case of a) I don't have cleared up my thoughts yet, but generally I
would like to know:
How are semantic extensions to work together in automated system?
Well, the semantics always defines some notion of entailment, and your
system is supposed to respect that notion: not draw invalid
conclusions, draw as many valid conclusions as you feel are useful,
don't say things are inconsistent when they aren't, etc.. Otherwise,
you have free rein. So, if you have several semantic extensions, they
are each provide a set of such entailments and they should add up to
one single set of legal entailments.
How to let agent know that the data is described using new RDF
extension, which the client doesn't know and the data could be (or
definitely are) false if it is interpreted using vanilla RDF
semantics?
NOt false, if its a semantic extension (they can't contradict the RDF
semantics., only extend it.) BUt same point more generally: how do we
know, given some RDF, what semantic extensions are appropriately to be
used when interpreting it? That is a VERY good question. This is
something that RDF2 could most usefully tackle, if only in a first-
step (ham-fisted?) kind of a way. We were aware that this was an issue
in the first WG, but it was just too far outside out charter, and our
energy level, to tackle properly. One obvious (?) thing to say is that
using a construction from a namespace which is associated with the
definition of any RDF semantic extension is deemed to bring along the
necessary interpretation conditions from the extension, so that for
example if I use owl:sameAs in some RDF, then I mean it to be
understood using the OWL semantic conditions. We all do this without
remarking upon it, but loosely, and to make this precise and normative
would be a very interesting (and useful) exercise. (An issue already
here is, which version of the OWL semantics is intended? Does the use
in RDF also "import" the OWL-DL syntactic restrictions on its use, for
example?)
Pat
b) How should my system know that the data which is just being
processed
is new revision of RDF/XML and not malformed RDF/XML when forward
compatibility was out of sight, out of mind when RDF/XML was designed?
Best,
Jiri Prochazka
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