- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Mon, 9 Jun 2003 12:10:00 -0400
- 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 UTC