Hector Levesque

Publications of Hector Levesque

• Progressing basic action theories with non-local effect actions (CS-2009)

  Authors: Stavros Vassos, Sebastian Sardina, Hector Levesque

  Ninth International Symposium on Logical Formalizations of Commonsense Reasoning (CS-2009), Toronto, Canada; 01/2009

  In this paper we propose a practical extension to some recent work on the progression of action theories in the situation calculus. In particular, we argue that the assumption of local-effect actionsIn this paper we propose a practical extension to some recent work on the progression of action theories in the situation calculus. In particular, we argue that the assumption of local-effect actions is too restrictive for realistic settings. Based on the notion of safe-range queries from database theory and just-in-time action histories, we present a new type of action theory, called range-restricted, that allows actions to have non-local effects with a restricted range. These theories can represent incomplete information in the initial database in terms of possible closures for fluents and can be progressed by directly updating the database in an algorithmic manner. We prove the correctness of our method and argue for the applicability of range-restricted theories in realistic settings.

• Progressing basic action theories with non-local effect actions (short paper PLS-2009)

  Authors: Stavros Vassos, Sebastian Sardina, Hector Levesque

  7th Panhellenic Logic Symposium (PLS-2009), Patras, Greece; 01/2009

  In this paper we propose a practical extension to some recent work on the progression of action theories in the situation calculus. Based on the notion of safe-range queries from database theory andIn this paper we propose a practical extension to some recent work on the progression of action theories in the situation calculus. Based on the notion of safe-range queries from database theory and just-in-time action histories, we present a new type of action theory, called range-restricted, that allows actions to have non-local e?ects with a restricted range. These theories can represent incomplete information in terms of possible closures for fluents and can be progressed by directly updating the database in an algorithmic manner.

• AAAI Outstanding Paper Honourable Mention Award (AAAI-2008)

  Authors: Stavros Vassos, Hector Levesque

  Association for the Advancement of Artificial Intelligence (AAAI); 01/2008

  The AAAI National Conference on Artificial Intelligence honors papers that exemplify the highest standards in technical contribution and exposition. During the blind review process, members of theThe AAAI National Conference on Artificial Intelligence honors papers that exemplify the highest standards in technical contribution and exposition. During the blind review process, members of the Program Committee recommend papers to consider for the Outstanding Paper Award. A subset of the Senior Program Committee, carefully chosen to avoid conflicts of interest, reviews all nominated papers and selects the winning paper(s). The paper that received the aformentioned award was the following: "On the Progression of Situation Calculus Basic Action Theories: Resolving a 10-year-old Conjecture" by Stavros Vassos and Hector J. Levesque.

• First-Order Strong Progression for Local-Effect Basic Action Theories (KR-2008)

  Authors: Stavros Vassos, Gerhard Lakemeyer, Hector Levesque

  11th International Conference on Principles of Knowledge Representation and Reasoning (KR-2008), Sydney, Australia; 01/2008

  In a seminal paper Lin and Reiter introduced the notion of progression for basic action theories in the situation calculus. The idea is to replace an initial database by a new set of sentences whichIn a seminal paper Lin and Reiter introduced the notion of progression for basic action theories in the situation calculus. The idea is to replace an initial database by a new set of sentences which reflect the changes due to an action. Unfortunately, progression requires secondorder logic in general. In this paper, we introduce the notion of strong progression, a slight variant of Lin and Reiter that has the intended properties, and we show that in case actions have only local effects, progression is always first-order representable. Moreover, for a restricted class of local-effect axioms we show how to construct a new database that is finite.

• On the Progression of Situation Calculus Basic Action Theories: Resolving a 10-year-old Conjecture (AAAI-2008)

  Authors: Stavros Vassos, Hector Levesque

  Twenty-Third AAAI Conference on Artificial Intelligence (AAAI-2008), Chicago, Illinois; 01/2008

  In a seminal paper, Lin and Reiter introduced a model-theoretic definition for the progression of the initial knowledge base of a basic action theory. This definition comes with a strong negativeIn a seminal paper, Lin and Reiter introduced a model-theoretic definition for the progression of the initial knowledge base of a basic action theory. This definition comes with a strong negative result, namely that for certain kinds of action theories, first-order logic is not expressive enough to correctly characterize this form of progression, and second-order axioms are necessary. However, Lin and Reiter also considered an alternative definition for progression which is always first-order definable. They conjectured that this alternative definition is incorrect in the sense that the progressed theory is too weak and may sometimes lose information. This conjecture, and the status of first-order definable progression, has remained open since then. In this paper we present two significant results about this alternative definition of progression. First, we prove the Lin and Reiter conjecture by presenting a case where the progressed theory indeed does lose information. Second, we prove that the alternative definition is nonetheless correct for reasoning about a large class of sentences, including some that quantify over situations. In this case the alternative definition is a preferred option due to its simplicity and the fact that it is always first-order.

• Progression of Situation Calculus Action Theories with Incomplete Information (IJCAI-2007)

  Authors: Stavros Vassos, Hector Levesque

  20th International Joint Conference on Artificial Intelligence (IJCAI-2007), Hyderabad, India; 01/2007

  In this paper, we propose a new progression mechanism for a restricted form of incomplete knowledge formulated as a basic action theory in the situation calculus. Specifically, we focus on functionalIn this paper, we propose a new progression mechanism for a restricted form of incomplete knowledge formulated as a basic action theory in the situation calculus. Specifically, we focus on functional fluents and deal directly with the possible values these fluents may have and how these values are affected by both physical and sensing actions. The method we propose is logically complete and can be calculated efficiently using database techniques under certain reasonable assumptions.