******************************************************************** ELECTRONIC NEWSLETTER ON REASONING ABOUT ACTIONS AND CHANGE Issue 97032 Editor: Erik Sandewall 12.12.1997 Back issues available at http://www.ida.liu.se/ext/etai/actions/njl/ ******************************************************************** ********* ETAI PUBLICATIONS ********* --- RECEIVED RESEARCH ARTICLES --- The following article has been *received* by the present ETAI area, which means that it will be open for a three-month discussion period, followed by the closed peer-review decision on whether it will be *accepted* by the ETAI. All readers of this Newsletter are invited to participate in the discussion. Questions and comments are sent to the present Newsletter editor, and will be included in forthcoming issues of the Newsletter. Past discussion is collected in structured form in the ETAI webpages. ======================================================== | AUTHOR: Jos Jlio Alferes, Joo A. Leite, Lus Moniz Pereira, Halina Przymusinska, and Teodor Przymusinski | TITLE: Dynamic Logic Programming | PAPER: http://www.ep.liu.se/ea/cis/1997/018/ | REVIEW: http://www.ida.liu.se/ext/etai/received/actions/005/aipf.html ======================================================== Please visit http://www.ida.liu.se/ext/etai/actions/nj/received.html for a list of all received articles in a plain web page, or http://www.ida.liu.se/ext/etai/actions/nj/recframe.html for a page using frames. --- 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: José Júlio Alferes, João A. Leite, Luís Moniz Pereira, Halina Przymusinska, and Teodor Przymusinski | TITLE: Dynamic Logic Programming ======================================================== -------------------------------------------------------- | FROM: Erik Sandewall -------------------------------------------------------- Dear Authors, Your paper addresses update of knowledge bases represented by logic programs - a topic which is known and understood by only a limited part of the reasoning about actions community. Because of the similarity of research goals and the difference of background, I think that a discussion between you as authors and the readers in our area is particularly important and valuable; it can hopefully facilitate very much the understanding of this specific work as well as the "school" that you represent. Towards the end of the paper, you explicitly mention "reasoning about actions" as one of the intended applications, which of course is of particular interest to us. Let me start out with a question about the prehistory of the approach you have chosen. You refer to Marianne Winslett's 1988 article [1] as an early reference for an "interpretation update" approach. Based on an example where it does not seem to give the intended result, you propose that the principle of inertia should be applied to the rules of the initial program rather than to the individual literals in a model. However, Winslett's article was written in response to an earlier article by Ginsberg and Smith [2] where they proposed exactly this: to define update on a set of logic formulae. Winslett pointed out some examples where the approach of Ginsberg and Smith did not work as intended, which is what led her to propose interpretation update. (An even earlier reference would of course be to the work by Lewis on counterfactuals [3]). My first question, therefore, is to what extent is there a difference: does your approach avoid the problems observed by Winslett, and if it does, what is the key to this improvement? My second question is with respect to updates in the presence of observations and action laws. One of your results is that if the initial program is just a set of facts, then program updates and model updates coincide. However, in the case of reasoning about actions, one typically deals both with facts about the world at various points in time ("observations") and with rules characterizing some of the effects of actions ("action laws", "effect laws"). If update methods are used for characterizing ramification, which is what Winslett's article was all about, then presumably one wishes to prefer changes of "facts" (that is, sign reversal of literals) over changes of the action laws, at least as a first approximation. Only in the presence of accumulated evidence is it reasonable to revise a well established action law. How would you foresee representing such cases: will action laws be written out explicitly as logic-program rules, and what updates will then be obtained on the current state? On the other hand, if action laws are not represented as rules, how are they represented and how are the results in your article to be used? Erik Sandewall [1] Marianne Winslett: Reasoning about actions using a possible models approach. Proc. AAAI 1988, pp. 89-93. [2] Matthew L. Ginsberg and David E. Smith: Reasoning about actions I: a possible worlds approach. In Frank M. Brown, ed, The Frame Problem in artificial intelligence, pp. 233-258. Morgan-Kaufmann, 1987. [3] D. Lewis: Counterfactuals. Harvard University Press, 1973. ******************************************************************** 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/ ********************************************************************