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Tim v. Bijan use case (was Re: Proposed issue:...)

From: Jim Hendler <hendler@cs.umd.edu>
Date: Fri, 3 Oct 2003 16:26:19 -0400
Message-Id: <p05200f20bba3863cd077@[172.27.173.28]>
To: Bijan Parsia <bparsia@isr.umd.edu>, Tim Berners-Lee <timbl@w3.org>
Cc: public-sw-meaning@w3.org

After banging about with this with Bijan for a while today (very 
inconclusively I'm afraid) I think we may have created a case for 
which Tim and Bijan would claim a difference - I'm not sure of this, 
but let's try -- it's essentially a slight expansion of the same use 
case I suggested the other day:

CONSIDER:

Document T defines Twin as a Class which has max cardinality 2 on 
property childOf.
   It defines Family01Twin as an instance of the class Twin.
   It also states A, B and C are all different individuals (As defined in OWL)


Document A defines T:A, T:B and T:C as all different individuals,
  it states T:A is a T:childOf  T:Family01Twin

Document B defines T:A, T:B and T:C as all different individuals,
  it states T:B is a T:childOf T:Family01Twin

Document C defines T:A, T:B and T:C as all different individuals,
  it say C is a T:childOf T:Family01Twin

The DISAGREEMENT:

Consider document D which imports A, B, and C   (but not T)
  Is document D consistent or inconsistent

  I believe Bijan would say Document D is consistent - the statements 
inherent on this document (all and only on the page created by the 
imports) contain nothing that is logically inconsistent.  The 
cardinality on T:Twin does not "influence" document D at all.

  I believe that Tim would say Document D is inconsistent (or at least 
that something was clearly wrong with it).  Since documents A, B and 
C clearly chose to use the T: definition of Twin, it should be 
assumed they are in agreement with it in some sense, therefore 
they've inherently agreed with the cardinality statement (otherwise 
they could have used some other URI to define their notion of Twin 
and ChildOf) and thus having three of these on the same document 
makes that Document inconsistent.

Note that if A, B, and C import T, then both Bijan and Tim would 
agree that document D is inconsistent, because the import would cause 
D to be logically "committed" (by the owl imports definition in S&AS) 
to the max cardinality of 2.


My personal dilemma is that I could go either way on this example - 
document D makes me uncomfortable (since A-C explicitly picked T: to 
use) but it doesn't seem like it should be considered as inconsistent 
as it should be in the imports case -- problem is being "a little 
inconsistent" is a lot like being "a little pregnant" it doesn't 
allow for much of a middle ground...

  -JH
p.s. Note there are many complex variants on this (what if A imports 
T, but B and C don't, etc.) but I was looking for the easiest example 
I could find where there was an explicit problem, all in the use of 
URIs with no need to invoke natural language...

-- 
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	  *** 240-277-3388 (Cell)
http://www.cs.umd.edu/users/hendler      *** NOTE CHANGED CELL NUMBER ***
Received on Friday, 3 October 2003 16:26:28 GMT

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