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Re: Rules WG -- draft charter -- NAF

From: Jim Hendler <hendler@cs.umd.edu>
Date: Fri, 14 Nov 2003 15:18:01 -0500
Message-Id: <p05200f1fbbdae5cff690@[10.0.1.5]>
To: Benjamin Grosof <bgrosof@mit.edu>, Sandro Hawke <sandro@w3.org>
Cc: adrianw@snet.net, www-rdf-rules@w3.org, phayes@ihmc.us

Ben-
  I agree w/Sandro - NAF requires identifying a set of facts it works 
over (the domain) - but RDF graphs,  but their very nature are open 
-- so what sound easy suddenly becomes very hard.  We attcked this 
problem in WebOnt (see our reqs document and issues lists - sorry, 
I'm on slow connection don't have the URIs, but they are one link 
from http://www.w3.org/2001/sw/WebOnt) - we wanted a way to have a 
local unique names assumption - but couldn't solve the problem -- I 
bet the local domain naming is at least as hard, probably harder
  here's an example, tell me whaty you would do

You say
  Rule1 - if person(shoesize) != large then A
  Rule2 - if person(shirtsize) != large then B
  RULES-CLOSED-OVER http://www.foo.bar/document1.rdf

and that seems fine,  but document1 includes
   :Joe owl:class :person.
   :Joe shoesize :large.
   :Joe nickname "the gorilla".
  :person rdf:type foo:human.

now, foo is a namespace document which contains a bunch of facts about humans.
It is clear that A is false, because the document you're closed over 
says his shoesize is large
But what about B being true?   We see that this document doesn't 
include that his shirtsize isn large, but what is on foo:?  Maybe it 
says anyone with the nickname "the gorilla" where's a large shirt, 
maybe it refers to another document, ad infinitum.
  So when there is a web of graphs refering to terms in other graphs, 
etc - how do you know where things stop?  (see www-sw-meaning for a 
lot more dicussion of this issue!)
  this is also only one simple manifestation of this problem -- when 
you talk about documents that are changing, scraped, etc. (all of 
which come up on the web) it gets even uglier

  Sandro put it well - it's not that we cannot do NAF, it's that 
designing the mechanism for definining the bounds of a graph on the 
web is still an unsolved problem -- if the rules group has to solve 
it to make progess, that is risky business....
  -JH
p.s. Note that the OWL group rjected the solution that we could use 
the imports closure and define everything else as not included, 
because that would limit you to only those things defined in the DL 
profile, not all OWL and all RDF documents -- the rules language 
would have to face that same issue, but also deal with all things 
findable by Xquery ... yow!
-- 
Professor James Hendler			  http://www.cs.umd.edu/users/hendler
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)
Received on Friday, 14 November 2003 15:18:02 UTC

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