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

From: Jim Hendler <hendler@cs.umd.edu>
Date: Thu, 5 Jun 2003 11:33:43 -0400
Message-Id: <p05200f55bb051187c1bf@[204.145.242.23]>
To: Christopher Welty <welty@us.ibm.com>, webont <www-webont-wg@w3.org>
```
At 10:58 AM -0400 6/5/03, Christopher Welty wrote:
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 - it's the linear nature of the above that causes a lot of the
problem.  Given a piece of RDF(S) there is no reason to expect it to
fall in Lite or DL unless you either have started from a particular
subset of RDFS or unless some work is done to check/make it
conformant.  For example, I would assume an OWL DL tool, given an
arbitrary piece of RDFS as input, would either need to run a
validator to see if it was appropriate, or would need to have some
sort of front-end that added annotations, typed some nodes, etc.
The point is the expectation should be that if you're already using
RDF and add a little bit of the OWL vocabulary to what you're doing,
you're likely to be in Full (which is fine).  If you then want the
reasoning gaurantees, you would do some work to learn about, and put
your documents into, Lite or DL.
We need to set that expectation -- the exact labels on the fragment
of RDFS aren't the important thing.  It's also worth noting that we
don't seem to have a place where someone can look to see what the
restrictions are that create the decidable (or FO or whatever)
fragment of RDFS, and that is a problem that we will eventually need
to fix (i.e. by adding Sean's document on RDF graphs to our stuff
somewhere, or the like)
-JH

--
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler
```
Received on Thursday, 5 June 2003 11:33:59 UTC

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