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WOWG: Response to HP -- some changes (Guide, Overview, Ref) we may need to make

From: Jim Hendler <hendler@cs.umd.edu>
Date: Mon, 9 Jun 2003 12:10:00 -0400
Message-Id: <p05200f14bb0a5e1524c8@[10.0.1.2]>
To: webont <www-webont-wg@w3.org>

In working on my new version of my response to Martin Merry, I tried 
to answer his concern that:

so we believe that if the documents made clearer that using BOTH 
oneOf and inverseOf (and their various forms) could lead to an 
unexpected rise in complexity, we would set the expectation 
correctly. In that way the current OWL DL subset would be easier to 
understand, and the design rationale behind it better understood.

Thus, given these two below, we propose that the WebOntology working 
group will make the issue above clearer and will write text to appear 
in the Reference, S&AS and Test documents that explain the above.

by quoting from Ref, Guide and Overview.  However, what I found in 
those three is that as we've currently written it, Ref captures the 
real situation better than the other two -- but we recommend people 
read the other two first.  In addition, the way that Guide and 
Overview describe DL v. Lite could be fixed to better handle the 
above. Also, S&AS, which should have a "definitive" statement on this 
doesn't.  This would help a lot to add

Here are my suggestions for all of these -- Editors, please let me 
know if you accept these changes (or similar ones of your own 
chosing), if not, we will need to schedule telecon time to discuss.
  thanks
  JH


---FIXING GUIDE ----

Specifically, Guide reads (Section 1.1)

OWL DL supports those users who want the maximum expressiveness 
without losing computational completeness (all entailments are 
guaranteed to be computed) and decidability (all computations will 
finish in finite time) of reasoning systems. ... OWL DL was designed 
to support the existing Description Logic business segment and has 
desirable computational properties for reasoning systems.

which is true, but that last sentence does seem to imply efficiency 
rather than decidability (since the first sentence mentions 
decidability).

but OWL Lite reads:

OWL Lite supports those users primarily needing a classification 
hierarchy and simple constraint features. ... . It should be simpler 
to provide tool support for OWL Lite than its more expressive 
relatives, and provide a quick migration path for thesauri and other 
taxonomies.

but doesn't mention complexity.

I suggest that we delete the last line of the DL description, and add 
the following line (from the Reference) to the Lite Description:

(Reference section 8.3)
The limitations on OWL Lite place it in a lower complexity class than 
OWL DL. This can have a positive impact on the efficiency of complete 
reasoners for OWL Lite.

This would help set appropriate expectations qua the issues brought up by Merry


----- Fixing Overview --------

Overview reads:

(section 1.3)
OWL Lite supports those users primarily needing a classification 
hierarchy and simple constraints. For example, while it supports 
cardinality constraints, it only permits cardinality values of 0 or 
1. It should be simpler to provide tool support for OWL Lite than its 
more expressive relatives, and OWL Lite provides a quick migration 
path for thesauri and other taxonomies.

I would add a sentence that reads:  "Owl Lite also has a lower formal 
complexity than OWL DL, see <reference section 8.3> for further 
details."

This would also help in addressing Merry's issues.

-------- Fixing S&AS -------

S&AS, since it is targeted to the expert, would be an obvious place 
to include some technical details of the distinction between Lite and 
DL from a complexity point of view.  I believe the introduction could 
easily add a paragraph stating that OWL FUll is undecidable, OWL DL 
is decidable but in complexity class NexpSpace (or whatever), and OWL 
Lite is decidable and in complexity class ExpSpace.

It might even be worth saying that the combination of inverses and 
individuals (oneOf, hasValue) lead to the extra complexity for OWL DL.


======================
-- 
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, 9 June 2003 12:10:36 GMT

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