Re: Where DAML+OIL deviates from the RDF-Schema spec.

At 1:37 PM -0500 3/1/01, Dan Brickley wrote:
>I agree with [2] and [3], and could live with [1]. My main concern w.r.t.
>using loops in the class and property hierarchies to indicate synonyms is
>with end-user comprehensibility and with user interface generation. I can
>see that there's a _logical_ story to tell about why loops are OK; I'm not
>so sure there's a modelling and usability story. But then it's not up to
>the core RDFS system to guarantee that folk can't make goofy modelling
>decisions, I guess.
>
>Dan
>

I'm with DanB on this one.  I originally proposed that if we wanted 
to use loops to assert equality, we'd lose the ability to (1) 
distinguish intentional from unintentional loops, and (2) force 
developers to understand the logical relationship (which I know from 
experience ain't always easy). In fact,
I was reminded later by one of my former postdocs that this situation 
has come up in practice in our experience -- we developed some of our 
KBs for the Parka-DB project using web-scrapers from online 
taxonomies and thesauri.  We saw a number of cases where loops 
existed - unintentionally, so we had to write loop breaking code in 
our systems -- under [1] we'd have trouble distinguishing the 
accidental from the intentional.

  I argued we should have a language construct that was explicit to 
assert equality.  I was overruled on the grounds that having two ways 
to do the same thing in a language was bad (Dan Connolly) and that 
DAML+OIL had to have the cycles for their associated logic engine  to 
handle this stuff (Ian Horrocks/Peter Patel-Schneider) -- as a 
result, my personal theorem prover was faced with
  a. Two equivalent solutions are bad
  b. We had to have solution [1]
and therefore, using the stuff that will power the semantic web
I was forced to conclude
  c. We should have [1] and only [1]

If someone is willing to remove assumption a or b, I would think we'd 
end up with something that makes more sense to the logically 
challenged folks (like me) who really want to use this stuff do to 
"frame"-like reasoning more than logical inference, or who would make 
errors that would cause whole chains of subclass relationships to 
collapse by accident.
   cheers
  Jim H
p.s. Parka-DB: http://www.cs.umd.edu/projects/plus/Parka/parka-db.html


At 11:53 PM +0100 2/24/01, Frank van Harmelen wrote:
>
>[1]
>"Warning: The RDF Schema specification demands that the 
>subclass-relation between classes
>must be acyclic. We believe this to be too restrictive, since a 
>cycle of subclass
>relationships provides a useful way to assert equality between 
>classes. Consequently,
>DAML+OIL places no such restriction on the subClassOf relationship 
>between classes;"

Dr. James Hendler		jhendler@darpa.mil
Chief Scientist, DARPA/ISO	703-696-2238 (phone)
3701 N. Fairfax Dr.		703-696-2201 (Fax)
Arlington, VA 22203		http://www.cs.umd.edu/~hendler

Received on Thursday, 1 March 2001 16:39:26 UTC