The talk was based on the following workshop paper I presented at AIIDE-2011: The SimpleFPS Planning Domain: A PDDL Benchmark for Proactive NPCs.

The details of the talk can be found here. The slides of my presentation can be found here.

Abstract:
In this paper we study the progression of situation calculus action theories that are able to handle a class of actions that, while extremely simple conceptually and common in many settings, cannot be handled by previous approaches. Specifically, based on the notion of safe-range queries from database theory and just-in-time action histories, we present a new type of action theories that ensures that actions have bounded effects over a restricted range of objects. Such theories may represent incomplete information and can be progressed by directly updating the knowledge base in an algorithmic manner.

Bibtex:

@inbook{vassos11hectorfest,
author = {Vassos, Stavros and Sardina, Sebastian},
booktitle = {Knowing, Reasoning, and Acting: Essays in Honour of Hector J. Levesque},
editor = {Lakemeyer, Gerhard and McIlraith, Sheila},
publisher = {College Publications},
title = {A Database-type Approach for Progressing Action Theories with Bounded Effects},
year = {2011}
}

Bibtex:

@inproceedings{vassos11simplefps,
author = {Vassos, Stavros and Papakonstantinou, Michail},
booktitle = {AIIDE 2011 Workshop on Non Player Character AI},
location = {Stanford, California, USA},
month = oct,
title = {The {SimpleFPS} Planning Domain: A {PDDL} Benchmark for Proactive {NPCs}},
year = {2011}
}

The slides of my talk (in Greek) can be found  here and the PDDL files mentioned in the talk can be found here. The planner used for the demo is BlackBox which can be found here (for windows use this executable and install the Cygwin DLL or make sure that cygwin1.dll is at the same folder as the BlackBox executable).

The abstract of the talk follows (in Greek).

Πρώτο μέρος: Εισαγωγή στην αναπαράσταση προβλημάτων σχεδιασμού (planning) με βάση τη γλώσσα STRIPS. Προέλαση, οπισθοχώρηση, και ευρετικές συναρτήσεις για την εύρεση λύσης σε προβλήματα σχεδιασμού με βάση την αναζήτηση. Αναπαράσταση προβλημάτων σχεδιασμού στην τυπική γλώσσα PDDL και χρήση του planner BlackBox για την επίλυση προβλημάτων σχεδιασμού στο πεδίο του puzzle game Sokoban.

Δεύτερο μέρος: Εισαγωγή στην ανάπτυξη τεχνητής νοημοσύνης για χαρακτήρες (non-player characters) σε video games και εφαρμογές τεχνικών σχεδιασμού σε εμπορικά video games. Αναπαράσταση των βασικών στοιχείων ενός First-Person Shooter game σε PDDL από την οπτική ενός αντίπαλου χαρακτήρα στον κόσμο του παιχνιδιού, και χρήση του planner BlackBox για την επίλυση προβλημάτων σχεδιασμού που σχετίζονται με τις επιλογές του χαρακτήρα στο παιχνίδι. Σύντομος σχολιασμός επιπλέον τεχνικών όπως η παρακολούθηση εκτέλεσης και ο επανασχεδιασμός.

The 9th International Workshop on Nonmonotonic Reasoning, Action and Change (NRAC-2011) will be held as part of the workshop programme of the 2011 International Joint Conference on Artificial Intelligence (IJCAI-2011) at Barcelona, Spain, in July 2011.

NRAC is a well-established forum for researchers interested in sharing their experiences in work in the areas of Nonmonotonic Reasoning, Reasoning about Action, and Belief Revision. An intelligent agent exploring a rich, dynamic world, needs cognitive capabilities in addition to basic functionalities for perception and reaction. The abilities to reason nonmonotonically, to reason about actions, and to change one’s beliefs, have been identified as fundamental high-level cognitive functions necessary for common sense. Research in all three areas has made significant progress during the last two decades of the past century. It is, however, crucial to bear in mind the common goal of designing intelligent agents. Researchers should be aware of advances in all three fields since often advances in one field can be translated into advances in another. Many deep relationships have already been established between the three areas and the primary aim of this workshop is to further promote this cross-fertilization.
This workshop will bring together researchers with the aim to:

• Compare and evaluate existing formalisms.
• Report on new developments.
• Identify the most important open problems and research questions.
• Identify possibilities of solution transferral between the areas.
• Identify important challenges for the advancement of the areas.
• Discuss challenges encountered when applying techniques in applications.

For more information visit the website of NRAC-2011 and the ResearchGate page of NRAC-2011.

Abstract:
In this thesis we study a reasoning module for agents that have cognitive abilities, such as memory, perception, action, and are expected to function autonomously for long periods of time. The module provides the ability to reason about action and change using the language of the situation calculus and variants of the basic action theories. The main focus of this thesis is on the logical problem of progressing an action theory.

First, we investigate the conjecture by Lin and Reiter that a practical first-order
definition of progression is not appropriate for the general case. We show that Lin and Reiter were indeed correct in their intuitions by providing a proof for the conjecture, thus resolving the open question about the first-order definability of progression and justifying the need for a second-order definition.

Then we proceed to identify three cases where it is possible to obtain a first-order progression with the desired properties: i) we extend earlier work by Lin and Reiter and present a case where we restrict our attention to a practical class of queries that may only quantify over situations in a limited way; ii) we revisit the local-effect assumption of Liu and Levesque that requires that the effects of an action are fixed by the arguments of the action and show that in this case a first-order progression is suitable; iii) we investigate a way that the local-effect assumption can be relaxed and show that when the initial knowledge base is a database of possible closures and the effects of the actions are range-restricted then a first-order progression is also suitable under a just-in-time assumption.

Finally, we examine a special case of the action theories with range-restricted effects and present an algorithm for computing a finite progression. We prove the correctness and the complexity of the algorithm, and show its application in a simple example that is inspired by video games.

Bibtex:

@phdthesis{vassos09phdthesis,
address = {Toronto, Canada},
author = {Vassos, Stavros},
school = {University of Toronto},
title = {A Reasoning Module for Long-Lived Cognitive Agents},
year = {2009}
}

Typos:

• Page 38,  point 5, last equation:  ”s less-than do(a,s’)” should be  ”s less-or-equal-than do(a,s’)”.
• Page 175, second paragraph, last sentence:  ”Unfortunately we can no longer then assume that D_una” should be “Unfortunately we can no longer then assume that D_alpha”.

Bibtex:

@inproceedings{vassos09rangerestricted,
address = {Toronto, Canada},
author = {Vassos, Stavros and Sardina, Stavros and Levesque, Hector},
booktitle = {Proceedings of the Ninth International Symposium on Logical Formalizations of Commonsense Reasoning (CS-09)},
editor = {Lakemeyer, Gerhard and Morgenstern, Leora and Williams, Mary-Anne},
pages = {135–140},
publisher = {UTSePress},
title = {Progressing basic action theories with non-local effect actions},
year = {2009}
}

Bibtex:

@inproceedings{vassos09localeffect,
address = {Sydney, Australia},
author = {Vassos, Stavros and Lakemeyer, Gerhard and Levesque, Hector},
booktitle = {Proceedings of 11th International Conference on Principles of Knowledge Representation and Reasoning (KR-08)},
editor = {Brewka, Gerhard and Lang, J{\’{e}}r{\^{o}}me},
pages = {662–672},
publisher = {AAAI Press},
title = {First-Order Strong Progression for Local-Effect Basic Action Theories},
year = {2009}
}

This paper was selected for the “Outstanding Paper Honorable Mention Award” in the Twenty-Third AAAI Conference on Artificial Intelligence!
Click here for more details about the award.

Abstract:
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.

Bibtex:

@inproceedings{vassos08conjecture,
author = {Vassos, Stavros and Levesque, Hector},
booktitle = {Proceedings of the Twenty-Third AAAI Conference on Artificial Intelligence (AAAI-08)},
location = {Chicago, Illinois, USA},
month = {July},
pages = {1004–1009},
title = {On the Progression of Situation Calculus Basic Action Theories: Resolving a 10-year-old Conjecture},
year = {2008}
}