Stavros Vassos

Publications

• The SimpleFPS Planning Domain: A PDDL Benchmark for Proactive NPCs (NPCAI-2011)

  Stavros Vassos, Michail Papakonstantinou

  Non-Player Character AI workshop of the Artificial Intelligence & Interactive Digital Entertainment (AIIDE) Conference (NPCAI-2011), Stanford, Palo Alto, California; 01/2011

  In this paper we focus on proactive behavior for non-player characters (NPCs) in the first-person shooter (FPS) genre of video games based on goal-oriented planning. Some recent approaches for applying real-time planning in commercial video games show that the existing hardware is starting to follow... [more] In this paper we focus on proactive behavior for non-player characters (NPCs) in the first-person shooter (FPS) genre of video games based on goal-oriented planning. Some recent approaches for applying real-time planning in commercial video games show that the existing hardware is starting to follow up on the computing resources needed for such techniques to work well. Nonetheless, it is not clear under which conditions real-time efficiency can be guaranteed. In this paper we give a precise specification of SimpleFPS, a STRIPS planning domain expressed in PDDL that captures some basic planning tasks that may be useful in a first-person shooter video game. This is intended to work as a first step towards quantifying the performance of different planning techniques that may be used in real-time to guide the behavior of NPCs. We present a simple tool we developed for generating random planning problem instances in PDDL with user defined properties, and show some preliminary results based on SimpleFPS instances that vary in the size of the domain and two well-known planners from the planning community.

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• A Database-type Approach for Progressing Action Theories with Bounded Effects (Book chapter)

  Stavros Vassos, Sebastian Sardina

  01/2011;

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• Challenges for Qualitative Spatial Reasoning in Linked Geospatial Data (BASR-2011)

  Manolis Koubarakis, Kostis Kyzirakos, Manos Karpathiotakis, Charalampos Nikolaou, Michael Sioutis, Stavros Vassos, Dimitrios Michail, Themistoklis Herekakis, Charalampos Kontoes, Ioannis Papoutsis

  IJCAI 2011 Workshop on Benchmarks and Applications of Spatial Reasoning (BASR-2011), Barcelona, Spain; 01/2011

  Linked geospatial data has recently received attention, as researchers and practitioners have started tapping the wealth of geospatial information available on the Web. We discuss some core research problems that arise when querying linked geospatial data, and explain why these are relevant for the ... [more] Linked geospatial data has recently received attention, as researchers and practitioners have started tapping the wealth of geospatial information available on the Web. We discuss some core research problems that arise when querying linked geospatial data, and explain why these are relevant for the qualitative spatial reasoning community. The problems are presented in the context of our recent work on the models stRDF and stSPARQL and their extensions with indefinite geospatial information.

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• A Reasoning Module for Long-Lived Cognitive Agents (PhD 2009)

  Stavros Vassos

  01/2009

  Degree: Doctor of Philosophy (Ph.D)

  Supervisor: Hector J. Levesque

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

  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 actions is too restrictive for realistic settings. Based on the notion of safe-range queries from database t... [more] 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 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)

  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 and just-in-time action histories, we present a new type of action theory, called range-restricted, that ... [more] 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 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)

  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 the Program Committee recommend papers to consider for the Outstanding Paper Award. A subset of the Senior ... [more] 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 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)

  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 which reflect the changes due to an action. Unfortunately, progression requires secondorder logic in genera... [more] 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 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)

  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 negative result, namely that for certain kinds of action theories, first-order logic is not expressive enough to ... [more] 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 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)

  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 functional fluents and deal directly with the possible values these fluents may have and how these values are a... [more] 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 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.

• A Feasible Approach to Disjunctive Knowledge in Situation Calculus (MSc 2005)

  Stavros Vassos

  01/2005

  Degree: Master of Science (M.Sc.)

  Supervisor: Hector J. Levesque

• The Wumpus World in IndiGolog: A Preliminary Report (NRAC-2005)

  Sebastian Sardina, Stavros Vassos

  Nonmonotonic Reasoning, Action and Change Workshop at IJCAI (NRAC-2005), Edinburgh, Scotland; 01/2005

  This paper describes an implementation of the the Wumpus World in IndiGolog with the objective of showing the applicability of this interleaved agent programming language for modeling agent behavior in realistic domains. We briefly go over the IndiGolog architecture, explain how we can reason about ... [more] This paper describes an implementation of the the Wumpus World in IndiGolog with the objective of showing the applicability of this interleaved agent programming language for modeling agent behavior in realistic domains. We briefly go over the IndiGolog architecture, explain how we can reason about the Wumpus World domain, and show how to express agent behavior using high-level agent programs. Finally, we discuss initial empirical results obtained as well as challenging issues to be resolved.

• Nonmonotonic Logical Approaches for the Frame Problem in Artificial Intelligence (Diploma 2001)

  Stavros Vassos

  01/2001

  Degree: Diploma

  Supervisor: Stathis Zachos