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Re: LANG: need to CLOSE Issue 5.6 Imports as magic syntax

From: Jim Hendler <hendler@cs.umd.edu>
Date: Sat, 2 Nov 2002 21:11:32 -0500
Message-Id: <p0511170bb9ea221081b7@[10.0.1.2]>
To: www-webont-wg@w3.org
Cc: Sandro Hawke <sandro@w3.org>

*** Chair Hat Off ***

I've spent a lot of time this week grappling with the issue of 
imports, talked to a lot of people, and reread all the emails and a 
number of discussions on RDFIG.  Based on all this I'm reluctantly 
forced to concur with Dan that the right thing for us to do is to 
POSTPONE this issue.  The rest of this message tries to explain my 
opinion.

----
To start with, lets create a very simple ontology I need for an 
example (I'll use N3 to save space):

<> a owl:ontology.
:animal a owl:class.
:person a owl:class.
:dog owl:sunClassOf :animal.
:owns a rdfs:property;
   rdfs:domain :person;
   rdfs:range :animal.
:Dan :owns :dog.

So if you read this document and I ask you "Do you believe there is 
someone who owns an animal" then if you trust the document, you 
should agree with this statement.

---
case 1
  Suppose we now make a slight change to the ontology.  There is a 
public file with information about people who work at the W3C (the 
actual file is at [1]) which we will call W3Cfile: for short.  So 
instead of

:Dan :owns :dog.
I replace it with
W3Cfile:Connolly :owns :dog.         # skip some details of fixing 
the namespace

now, I ask you "Do you believe someone from the W3C owns an animal". 
Seems to me to say Yes to this, you need to believe my document and 
also to believe W3Cfile.  If you don't believe W3Cfile,  but you do 
believe my document, you would say "I believe someone owns an animal, 
but I'm not yet convinced this is someone from the W3C."

-----
case 2
  Jeff makes an extremely important point - suppose we do want to make 
it so that you should believe someone from the W3C owns a dog just by 
believing my document -- then if I include in my document

<> owl:imports W3Cfile:.

(and we do something similar to what Peter suggests) it would be a 
way of saying my document trusts everything in the W3Cfile, and 
therefore just by trusting me, you are convinced to believe someone 
from the W3C owns an animal.

Jeff is absolutely correct that this is an important feature of the 
Semantic Web.

--
However, here's the problem -- notice that I had to discuss this 
using terms like "believe" and "trust".  Further, there's a lot of 
other issues as well.  Consider, that I might want to say "I trust 
the W3C for issues relating to Dan Connolly, but not for anyone else" 
or "I don't trust how the W3C discusses animals, so ignore what they 
say about that and use my definitions," or... or ... or...

Putting words into Dan Connolly's mouth, he is worried that even 
though Jeff's concern might be legitimate, we run the risk of taking 
a meat cleaver approach to something that could be better handled 
with a scalpel -- by accepting this approach, we may discover later 
that we regret it, but lots of implementations would already relay on 
it - whereas if we focus on this issue in our research and 
implementations, at a later time we may be able to do a much more 
comprehensive and better solution and then make that normative. 
Also, it may be important to do this at the basic document level 
(i.e. in some RDF way) instead of in Owl per se.   I've come to agree 
with that, and therefore suggest POSTPONING.

----
btw, I have no objection to us doing something "non-normative" with 
respect to what Jeff and Peter have suggested.  I think if we put 
that into an Appendix (non-normative) or in a separate note (or a FAQ 
page) - I would not complain -- but making this definitive, I've come 
to believe Dan and his colleagues may be right.
  -JH
















[1] http://www.ece.umd.edu/~adityak/w3cpeople.rdf


-- 
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 Saturday, 2 November 2002 21:11:37 GMT

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