- From: Stephane Fellah <fellah@pcigeomatics.com>
- Date: Fri, 2 Jul 2004 14:38:03 -0400
- To: "Bijan Parsia" <bparsia@isr.umd.edu>
- Cc: <public-sws-ig@w3.org>
Bijan, Thanks for your detailed answer. I think it time to do my homework now. I will come back to you once I understand better the issue with second-order logic. The broken link for Cyc is (one line): http://www.cyc.com/doc/tut/ppoint/SecondOrderPredicates_files/frame.htm Best regards Stephane Fellah Web Chief Architect PCI Geomatics 490, Boulevard St Joseph Hull, Quebec Canada J8Y 3Y7 Tel: 1 819 770 0022 Ext. 223 Fax 1 819 770 0098 Visit our web site: www.pcigeomatics.com -----Original Message----- From: Bijan Parsia [mailto:bparsia@isr.umd.edu] Sent: Friday, July 02, 2004 1:25 PM To: Stephane Fellah Cc: public-sws-ig@w3.org Subject: Re: OWL-S: Parameter modeling On Jul 2, 2004, at 2:07 PM, Stephane Fellah wrote: > Bijan, > > Thanks for your detailed response. I understand now why I am in > OWL-Full. Basically the approach I suggest, is using second-order > predicate (meta-property). Well. you are using second-order *syntax*. You really don't want to go true second order. It's not only undecidable, but incomplete (in general), and fairly difficult to work with. First order logic is challenging enough :) Second order syntax has a lot of appeal, as you've pointed out. OWL Full is designed have that appeal without having the pain of full second order. However, this can cause other difficulties. I strongly recommend checking out Hilog. You also will find some nice, accessible discussion in: http://www.ihmc.us/users/phayes/SCL-december.html > Note that Cyc is also using working second-order logic reasoner using > second-order predicate. Ref. > http://www.cyc.com/doc/tut/ppoint/SecondOrderPredicates_files/ > frame.htm > What is wrong with their approach ? Sorry, that page isn't rendering for me. > I think when it comes to model function or process, adding the support > of second-order predicate in reasoners will simplify considerably the > description of process or functor. The question is whether this > addition of second-order predicate (a small subset of second-order > predicate logic) would keep the reasoner decidable and can compute in > a finite time. Most probably not, if you introduce true second order variables. However, this is exactly why OWL Full, HiLog, and common logic take the second order syntax, first order semantics approach. However, this causes them to *deviate* from the standard mapping into first order logic. For example, instead of classes being first place predicates, they are triples. (a rdf:type C). To get back the *class* semantics, you need an axiom (or many), if (a rdf:type C) then Ca. Getting the right axioms, and proving that they get it right, etc. etc. is tricky. I am working on some other ways to accomplish some of this. > Why should we stick religiously to DL ? It's not about religion, it's about accomodating various user communities, tools, existing reasoners. > Not being an implementer of inference engine, I am asking whether it > is a huge task to add this second order predicate extension in > existing DL reasoner or not ? Depends on how you do it. The OWL Full way, I'd say yes. It's all about trade offs. Personally, I wouldn't do this for readability. Have a surface language for that. Cheers, Bijan Parsia.
Received on Friday, 2 July 2004 14:38:34 UTC