******************************************************************** ELECTRONIC NEWSLETTER ON REASONING ABOUT ACTIONS AND CHANGE Issue 97019 Editor: Erik Sandewall 10.11.1997 Back issues available at http://www.ida.liu.se/ext/etai/actions/njl/ ******************************************************************** ********* TODAY ********* The ontologies panel continues unabated, today with a contribution by Hector Geffner. Also, the session on the paper by Kakas and Miller today contains the first occurrence of a continuation - beyond questions to the authors and answers to the questions, which we have had so far, there is a follow-up question posed by Alessandro Provetti. If you are using our web pages for referring to earlier discussion, you may appreciate that there is now a separate web page for each panel discussion. It is accessed via the HTML version of Newsletters (just click the session's headline in the Newsletter issue) or via the ordinary entries to the Actions and Change web structure. ********* ETAI PUBLICATIONS ********* --- DISCUSSION ABOUT RECEIVED ARTICLES --- The following debate contributions (questions, answers, or comments) have been received for articles that have been received by the ETAI and which are presently subject of discussion. To see the full context, for example, to see the question that a given answer refers to, or to see the article itself or its summary, please use the web-page version of this Newsletter. ======================================================== | AUTHOR: Antonis Kakas and Rob Miller | TITLE: Reasoning about Actions, Narratives and Ramification ======================================================== -------------------------------------------------------- | FROM: Alessandro Provetti -------------------------------------------------------- Dear Antonis and Rob, I'd like to comment on Tom's example about the role of h-statements in A-languages. In the language L of Baral et al. the theories: F at S0 and F at S0 A occurs_at S0 have different models. Assume that there are other fluents than F, the former has models which differ one to another by the interpretation of the initial state (except -of course- for F) while agreeing on the fact that nothing happened at all. The latter yields the same models as far as the initial state is concerned, BUT all of them sanction that A has happened. As a result, the latter theory implies the formula `A occurs_at S0.' It appears to me that the equivalence of the two theories above under E-semantics does not mean in general that A-style semantics cannot account for h-propositions. You may want to comment on this in the paper or -possibly- proceed to work on the entailment associated to E. Hope this helps. Ciao! Alessandro Provetti ********* DEBATES ********* --- NRAC PANEL DISCUSSION ON ONTOLOGIES FOR ACTIONS AND CHANGE --- -------------------------------------------------------- | FROM: Hector Geffner -------------------------------------------------------- Rob Miller says: My problem with this is that, in general, dynamical systems in the everyday world can't be realistically modelled as state transition systems, because they involve things like continuous change, actions or events with duration, partially overlapping events, interuptable events, etc. ... My point is that action languages - in any dress you like - are just a convenient means for specifying (and in certain cases reasoning with) dynamic systems. That is the main lesson I think of the Yale Shooting Problem(s) and a lot of the work on temporal non-mon. Namely, the meaning of a rule like: if loaded and shoot then not alive is that the only state trajectories s0, s1, s2, ..., that are possible are the ones in which `alive' is false at si+1 when loaded and shoot are true at si. You can formulate the idea in many ways (suitable circumscriptive policy, Erik's version of chronological minimization, predicate completion, ...), but it is the same idea: *rules specify possible state transitions*, *observations prune possible state trajectories*. Now, Rob is right; dynamic systems come in different varieties; e.g., 1. discrete time, discrete value space 2. discrete time, continuous value space 3. continuous time, continuous value space .... Rules like the one above (with first order extensions, etc) are good for specifying systems of Type 1 only. Yet it's not difficult to see how systems of Type 2 could be specified as well. Actually there are *other* type of mathematical models for the type of problems that Rob has in mind as the "Semi-Markov Decision Processes" (probabilistic continuous processes - like queuing systems - that are controlled at discrete time intervals). My point is that we are *not* inventing new mathematical models of dynamic systems. What we are inventing are suitable structured languages for specifying and in certain cases controlling those systems. That's what STRIPS is about. In my view, the KR/control enterprise is about developing richer versions of STRIPS suitable for specifying and controlling not only systems of Type 1, but also Markov Decision Processes, Partially Observable MDPs, Semi-MDP's, etc etc. How we will measure success? When we can model and control some dynamic systems that cannot even be modeled using non KR methods. - Hector Geffner ******************************************************************** This Newsletter is issued whenever there is new news, and is sent by automatic E-mail and without charge to a list of subscribers. To obtain or change a subscription, please send mail to the editor, erisa@ida.liu.se. Contributions are welcomed to the same address. Instructions for contributors and other additional information is found at: http://www.ida.liu.se/ext/etai/actions/njl/ ********************************************************************