- From: pat hayes <phayes@ai.uwf.edu>
- Date: Tue, 25 Feb 2003 12:45:30 -0600
- To: Tanel Tammet <tammet@staff.ttu.ee>
- Cc: Seth Russell <seth@robustai.net>, www-rdf-interest@w3.org
>pat hayes wrote: > >>> In particular I intend to providing the feed to Google in >>>support of their new Froogle service [3] and also to publish it >>>off my web site as an RDF feed. Were someone to use the RDF feed >>>to determine if I said that I could delive a particular product at >>>any given time, they would need to use a non-monotonic inference >>>process. >> >> >>Are you SURE it is nonmonotonic? If you are explicit about dates >>and what delivery date means, and if you have access to a >>clock/calendar as an external source of data, and if you time-stamp >>your information, then the overall pattern of reasoning can be >>monotonic. The nonmonotonicity will arise if you keep some or all >>of this under the hood, so to speak, and make inferences which >>depend on it, in fact, but do not openly acknowledge their >>dependency. > >It is actually very common for nonmonotonicity (of some kind) to >appear in simple and >obvious examples. Take an ordinary SQL-based database system and >start building FOL >extensions to it. Every table in a database is mapped to a predicate >in FOL. The intended >meaning of most (if not all tables) is that the correspoding >predicate is closed in the sense >that if P(a,b) does not appear in the table then it is not true. > >IMHO a suitable way to proceed in such cases is to use a "known" >predicate and a simple >form of knowledge logic. As we know, knowledge logics tend to be cover some >nonmonotonic logics, but are better and clearer way than a trivial >nonmononotonic logic: >intended meanings are explicit, not hidden. That is an interesting idea, can you elaborate on what particular kind of knowledge logic you mean? (Do you mean McCarthy-style circumscription? Certainly that has the advantage of keeping the nonmonotonicity kind of localized and easy to find.) >Since OWL and the whole semantic web area is actually very strongly >connected to >"ordinary" databases (that is where data is normally kept in >practice, that is the language >understood by programmers) I guess that guidelines for combining OWL and FOL >with databases is really crucial in practice. You are probably right. You might be interested in the ideas that Bill Anderson has been expounding. His company uses a formalism which is highly expressive (KIF, in effect) but which has an overall assumption of closed-world negation. This gives them a combination of expressiveness with effective computability, he claims. Unfortunately Bill is in the national guard and has been called into service, so you can't ask him directly just now. >In simple database-like cases the knowledge-predicate-encoded >queries tend to be >computable, since closed predicates tend to be used without function >symbols, hence >derivability is often computable. This sounds like the description logic path. The current discussions about rule systems often assume similar syntactic restrictions as well. >IMHO it will be possible to encode most of the >practical examples of the kind Seth brought using a knowledge >predicate while still keeping >computability of queries. That is a very interesting idea. You really should check up on the RuleML website and see what is being said there. >"Plain" nonmonotonic reasoning is bad. As we know, it does not work >without additional >mechanisms for priorities, which are normally ad hoc. Explicit >nonmonotonic reasoning >with a knowledge predicate is survivable. What I think will happen is that mechanisms to 'protect' nonmonotonic conclusions on the SW will evolve with use. Pat >Tanel Tammet -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes s.pam@ai.uwf.edu for spam
Received on Tuesday, 25 February 2003 13:45:33 UTC