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Re: Minutes of the beer session

From: Jim Hendler <hendler@cs.umd.edu>
Date: Mon, 26 May 2003 16:01:55 -0400
Message-Id: <p05200f08baf81cf160df@[10.0.1.2]>
To: Jeremy Carroll <jjc@hpl.hp.com>, webont <www-webont-wg@w3.org>
Cc: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>

Couple of responses
:

A small quantity of beer was drunk at Jim's expense by Peter and myself on
>Friday evening.

A "small" quantity? Do I get change :-> (actually, if all the below 
flies, it was money well spent!)

>
>We considered the following 7 issues:

[snipping]

issues A - C look fine

>
>D) OWL DL syntax NP complete
>
>Included in comments
>http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0083.html
>http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0052.html
>owlsas-rdfcore-np-complete
>
>Original message:
>http://lists.w3.org/Archives/Public/www-webont-wg/2003Apr/0003.html
>
>We agreed on solution 2 at the end of the original message.
>
>change mapping rule to
>EquivalentClasses( d1, .... dn )
>==>
>  T(dj) owl:equivalentClass T(di) .   For all i,j s.t {i,j} in G, an arbitrary
>connected graph over {1, 2, ... n }
>
>(Exact wording is editorial)
>We agreed that the expected reader of S&AS is also expected to understand
>terms from graph theory without any explanation, i.e. this rule will be
>opaque to the non-specialist.


I am not sure I understand the solution - does this make the mapping 
non-NP-complete by making it NP-hard or by moving it into a lower 
class :->?   Seriously,  I am not sure I understand why the solution 
above resolves the problem Jeremy brought up (the reduction of the 
mapping to a NP-complete graph problem) - I do know graph theory, but 
the above doesn't immediately make it clear why this fixed the 
problem.  I can live with that, but writing a response to the rdf 
core group and others will require an explanation as to how this 
fixes the problem.

>
>E) unnamed individuals
>http://lists.w3.org/Archives/Public/public-webont-comments/2003May/0052.html
>owlsas-rdfcore-bnodes-restrictions
>
>Peter and I propose we postpone this issue.
>Rationale:
>- the amount of work to do otherwise is large, and is not guaranteed to
>succeed.
>- however the point is a good one and should be reviewed once the community
>has more experience.
>
>(Personal note: my reading is that much of the approach taken in S&AS part 3
>would need substantial reworking to address this)
>

I think postponing makes sense - but I suspect we'll need something 
in our docs somewhere to talk about the implications -- hwoever, I 
think we're going to have to work harder to get all our docs to 
explain that RDF users should assume they will be using OWL Full 
unless they are willing to restrict their graphs - and then we need 
to explain the restrictions -- which probably means bringing that 
document of Jeremy's up to date or producing something else (see 
below) -  Brian McB, Eric M. and a few others indicated to me in 
Budapest that doing this would help address their concerns-  editors 
might want to think about thwre this explanation goes


>F) ambiguity

Just to confirm - you think the current solution is okay, but needs 
better explanation - and that would be localized to S&AS, is that 
right?

>
>G) OntologyProperty

works for me

>====
>
>We also discussed the issue of an alternative articulation of the mapping
>rules to go in the other direction. We were not convinced that these comments
>could be addressed with a relatively small amount of work. A possible
>approach is to sidestep them by pointing to two implementations of an OWL
>Syntax Checker (which we already have, modulo the last details). This is the
>initial proposal from the beer session.
>
>The possible additional text that we have is:
>- the description of RDF graphs as triples
>- the related proof (incomplete)
>
>The related proof does address the reverse mapping problem, but is unfinished
>and difficult to read. It does include tables (which I don't think I ever got
>round to generating) of when you see this triple then use this abstact syntax
>construct. The amount of work needed to get it finished is nontrivial.
>
>The description of RDF graphs as triples could be updated failry quickly, but
>only permits the building of a recognizer (an OWL Syntax Checker) and not a
>tool which outputs the abstract syntax tree.


How hard would it be to do a sort of "easy version" in the following 
sense - is there a subset of the OWL DL graphs that is easier to 
explain?  In Judaism we call these things "normative" practice (note 
the very different use of the word normative, which confused me no 
end for a while) -- normative practice is a set of rules that 
oversimplify complex things in a way that is easier to follow.  For 
example, the actual law in Judaism is something like
  "on the Sabbath you cannot write two or more letters next to each 
other with anything that either leaves a permanent mark whether it be 
ink or non-ink.  If the letters are written at separate times, and 
they are within certain size limitations, then (this goes on for 
about 7 pages)"
  the normative version is
"Don't write anything on Shabbat"

What I'm thinking it would be possible to have a useful set of rules 
that says "if you live by the following rules, your graphs will be in 
OWL DL.  There are other graphs which are also in DL, but are harder 
to explain in detail -- see S&AS for the full definition"

guess I'm wondering of such a thing is possible...


-- 
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 Monday, 26 May 2003 16:02:04 GMT

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