On Feb 4, 2009, at 6:34 PM, Chris Mungall wrote: (01)
>
> On Feb 4, 2009, at 1:43 PM, Pat Hayes wrote:
>
>>> It
>>> is essential that the representation is computer interpretable, as
>>> interoperability is the goal of IDEAS - still doesn't rule out
>>> barcoded body
>>> parts, you'll note.
>>>
>>> I still can't see RDFS and RDF as anything other than syntax
>>> (sorry, we
>>> might have to disagree on this)
>>
>> You are simply wrong about this. I'm not pulling rank or anything,
>> but RDF/S is pretty tightly described in the W3C specs, which are
>> quite clear on what parts are normative, and the model-theoretic
>> semantics is normative. So for example if you say that
>> rdfs:subClassOf is just syntax, so you will choose to interpret it
>> as the motherOf relation, then you are not using RDFS. You are using
>> RDFS syntax in some other, non-RDFS, way.
>
>
> I'm not sure Ian is 100% wrong. Or if he is wrong, then he is at least
> in good company. (02)
He certainly has company, unfortunately. (03)
> Where OWL is concerned, it's common to treat RDF as a
> syntax - perhaps just because it simplifies things tremendously. See
> for example:
>
> "OWL 2 Web Ontology Language: Mapping to RDF Graphs"
> http://www.w3.org/TR/2008/WD-owl2-mapping-to-rdf-20081202/
> "This document defines a mapping of OWL 2 ontology into the RDF
> **syntax**, and vice versa. "
> (04)
This is OWL 2, which is not the same as the original OWL
specifications. Don't call OWL 2 "OWL", they are different languages
with very different specs. (05)
> You'll have to forgive us mere mortals for getting confused here; it
> goes on to state "The syntax for triples used in this document is the
> one used in the RDF Semantics [RDF Semantics]" - which links to your
> document, which uses N-triples as the syntax. So is RDF a syntax? (06)
RDF has a syntax, yes. The RDF specs go on about this at length. The
normative RDF syntax is the abstract graph syntax, which can be given
a surface ('interchange') syntax in a variety of ways (N-triples, RDF/
XML, N3 are all viable alternatives, and anyone can invent one of
their own if they like, as long as they show how to parse it into an
RDF graph. (07)
> Why
> doesn't the OWL document say "defines a mapping of OWL 2 ontology into
> N-triples syntax"? (08)
I have no idea why the OWL2 documents say what they say, having had no
hand in their writing. In these email threads when I refer to OWL I
am referring to the original OWL specs. (09)
> There is a separate document for mapping to RDF semantics:
> http://www.w3.org/TR/2008/WD-owl2-rdf-based-semantics-20081202/
> "This document provides the RDF-compatible model-theoretic semantics
> for OWL 2, called "OWL 2 Full"
>
> But this can be ignored if one simply wants to use RDF/XML as a
> transport layer for OWL (which I'm guessing will become less common
> now there is a sensible XML syntax for OWL) (010)
Yes, Im sure that OWL will go its own way largely independently from
RDF. This was always the goal of the DL activists in the working
groups, especially Peter Patel-Schnieder, who published several
influential papers arguing for this early in the game, and was an
active and tireless opponent of making OWL itself RDF-compatible. THe
W3C working groups have always been mired in controversy about RDF:
many of the logically-trained folk detest it with a passion and see it
as a barrier to progress. OWL 2 is a product of a self-selected
working group which set out with that ambition in mind. I disagree,
myself, but I've given up trying to win academic/political fights over
this. I will work on RDF and the world can go to hell in its own way :-) (011)
>
>
> Now obviously the story is a little more complicated here, and it
> seems that the division between syntax and semantics is not entirely
> agreed upon. (012)
Really, this is quite clearly agreed upon. What isnt so clear is how
to relate two different syntaxes and semantics when one language (OWL-
n) is syntactically embedded in another (RDF). That is hard to do
accurately and elegantly, and its a lot easier if the OWL syntax in
RDF can simply ignore the RDF semantics, and impose its own meanings
onto that RDF-encoded syntax. I think the OWL 2 group could have done
a much better job of this than they did, in fact, but I suspect they
weren't motivated to try very hard. Part of what I want to to do in
improving RDF is to make this kind of embedding of one language into
another easier to state: the trick is to treat the RDF meaning of the
OWL-n syntax as being an RDF metatheory of the OWL syntax. We didn't
think of this when we did the OWL specs. (013)
> But there is nothing to stop Ian defining a similar
> mapping for his language, performing tricks such as making rdf:type
> triples disappear into the ether. (014)
IT is quite legal to simply not use rdf:type, of course. What isnt
legal is to use it to mean something different from what the spec says
it means. But if Ian wants to use ian:type instead of rdf:type, he is
free to do so and that is a perfectly legal use of RDF. I suspect this
is what he means, in fact. (015)
> I guess you could say that the OWL
> folks are "using RDF syntax (particularly rdf:type) in some other non-
> RDF way" - if so, is that bad? (016)
IMO, yes. It will produce a split between the RDF-using semantic web
and the DL-OWL-using semantic web. I have been expecting this to occur
for some time. I myself am chiefly interested in the RDF SWeb. (017)
But all this W3C-internal bickering aside, it is both wrong and a
violation of the RDF normative specifications to say that RDF and RDFS
have no semantics. Anyone can of course use anything in a way that
violates the specifications: I can use XML to encode octal
representations of musical notation if I like. BUt doing this is
misusing, rather than using, XML.
>
> Personally I don't really see the point, but I just thought I'd point
> out that Ian isn't in the minority here.
>
> Cheers
> Chris
>
>
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