Re: WOWG: Report from WWW 2003 - OWL presentation/issues

Jeremy,

I've argued this with Pat several times.  I'd like to see an authoritative 
definition of what "first-order" means, otherwise we're all using our own 
definitions.  In any dictionary of logic or philosophy or mathematics that 
I've been able to find, "first-order" is defined as "not higher order" and 
"higer order" is defined as predication of predicates (or functions of 
functions).

Until someone produces an authoritative definition of first-order that 
says something else, I don't think it's ever "simply incorrect" to call 
RDFS higher-order.   It is "simply" correct.  It may be incorrect 
according to your (or Pat's) more complicated definition of what 
first-order means, but that is by no means "simple"!

I have claimed from the start that a useful distinction here is to say 
that RDFS is syntactically higher-order and semantically first-order.  Pat 
has not agreed.

More to the point, I believe it to be the case that RDFS is undecidable 
(has this been proven?), and certainly OWL DL is decidable (has this been 
proven?).  Therefore I think it may be more useful to make the diagram 
look like this:

RDFS -> (decidable fragment of RDFS) -> OWL Lite -> OWL DL -> OWL Full
  +--------------------------------------------------------------^


-Chris

Dr. Christopher A. Welty, Knowledge Structures Group
IBM Watson Research Center, 19 Skyline Dr., Hawthorne, NY  10532     USA   
 
Voice: +1 914.784.7055,  IBM T/L: 863.7055, Fax: +1 914.784.6912
Email: welty@us.ibm.com, Web: http://www.research.ibm.com/people/w/welty/




Jeremy Carroll <jjc@hplb.hpl.hp.com>
Sent by: www-webont-wg-request@w3.org
05/29/2003 03:28 AM
 
        To:     Jim Hendler <hendler@cs.umd.edu>
        cc:     Dan Connolly <connolly@w3.org>, Ian Horrocks 
<horrocks@cs.man.ac.uk>, webont <www-webont-wg@w3.org>
        Subject:        Re: WOWG: Report from WWW 2003 - OWL 
presentation/issues





Jim Hendler wrote:


>>>  The reality of our design is more like:
>>>
>>>      [OWL Full]
>>>      /        \
>>>  [RDFS]      [OWL DL]
>>>      \       [OWL Lite]
>>>       \       /
>>>  [FO fragment of RDFS]
>>
>>
>> That's a nifty diagram. I like that.


Me too, for the diagram, but I disagree with the FO part of FO fragment of 

RDFS. Simply [fragment of RDFS] would do. As I understand it, the intent 
is 
that this is merely the intersection of OWL Lite and RDFS.

The FO bit is questionable: RDFS is first order, just Ian prefers looking 
at it in a different way, and insists on calling something that does not 
map classes into (well-founded) sets as non-first order, which, as far as 
I 
can tell, is simply incorrect.

Jeremy