Research Group on the Foundations of Artificial Intelligence

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2009

• Florian Pommerening, Stefan Wölfl and Matthias Westphal.
  Right-of-Way Rules as Use Case for Integrating GOLOG and Qualitative Reasoning.
  In Bärbel Mertsching, Marcus Hund and Muhammad Zaheer Aziz, Proceedings of the 32nd Annual Conference on Artificial Intelligence (KI 2009), pp. 468-475. Springer-Verlag 2009.
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  Agents interacting in a dynamically changing spatial environment often need to access the same spatial resources. A typical example is given by moving vehicles that meet at an intersection in a street network. In such situations right-of-way rules regulate the actions the vehicles involved may perform. For this application scenario we show how the Golog framework for reasoning about action and change can be enhanced by external reasoning services that implement techniques known from the domain of Qualitative Spatial Reasoning.

• Matthias Westphal and Stefan Wölfl.
  Qualitative CSP, finite CSP, and SAT: Comparing methods for qualitative constraint-based reasoning.
  In Proceedings of the 21th International Joint Conference on Artificial Intelligence (IJCAI 2009). 2009.
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  Qualitative Spatial and Temporal Reasoning (QSR) is concerned with constraint-based formalisms for representing, and reasoning with, spatial and temporal information over infinite domains. Within the community it has been a widely accepted assumption that genuine qualitative reasoning methods outperform other reasoning methods that are applicable to encodings of qualitative CSP instances. Recently this assumption has been tackled by several authors, who proposed to encode qualitative CSP instances as finite CSP or SAT instances. In this paper we report on the results of a broad empirical study in which we compared the performance of several reasoners on instances from different qualitative formalisms. Our results show that for small-sized qualitative calculi (e.g. Allen's interval algebra and RCC-8) a state-of-the-art implementation of QSR methods currently gives the most efficient performance. However, on recently suggested large-size calculi, e.g. OPRA_4, finite CSP encodings provide a considerable performance gain. These results confirm a conjecture by Bessière stating that support-based constraint propagation algorithms provide better performance for large-sized qualitative calculi.

• Stefan Wölfl and Matthias Westphal.
  On combinations of binary qualitative constraint calculi.
  In Proceedings of the 21th International Joint Conference on Artificial Intelligence (IJCAI 2009). 2009.
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  Qualitative constraint calculi are representation formalisms that allow for efficient reasoning about spatial and temporal information. Many of the calculi discussed in the field of Qualitative Spatial and Temporal Reasoning can be defined as combinations of other, simpler and more compact formalisms. On the other hand, existing calculi can be combined to a new formalism in which one can represent, and reason about, different aspects of a domain at the same time. For example, Gerevini and Renz presented a loose combination of the region connection calculus RCC-8 and the point algebra: the resulting formalism integrates topological and qualitative size relations between spatially extended objects. In this paper we compare the approach by Gerevini and Renz to a method that generates a new qualitative calculus by exploiting the semantic interdependencies between the component calculi. We will compare these two methods and analyze some formal relationships between a combined calculus and its components. The paper is completed by an empirical case study in which the reasoning performance of the suggested methods is compared on random test instances.

• Bernhard Nebel and Stefan Wölfl.
  Benchmarking of Qualitative Spatial and Temporal Reasoning Systems.
  2009.
  AAAI Technical Report SS-09-02.
  (AAAI)
  

• Matthias Westphal and Stefan Wölfl.
  Confirming the QSR Promise.
  In AAAI Spring Symposium on Benchmarking of Qualitative Spatial and Temporal Reasoning Systems. 2009.
  AAAI Technical Report SS-09-02.
  

• Matthias Westphal, Stefan Wölfl and Zeno Gantner.
  GQR: A Fast Solver for Binary Qualitative Constraint Networks.
  In AAAI Spring Symposium on Benchmarking of Qualitative Spatial and Temporal Reasoning Systems. 2009.
  AAAI Technical Report SS-09-02.
  

2008

• Christian Freksa, Nora Newcombe, Peter Gärdenfors and Stefan Wölfl.
  Spatial Cognition VI: Learning, Reasoning, and Talking about Space, International Conference Spatial Cognition 2008, Freiburg, Germany, September 15-19, 2008.
  Volume 5248 of Lecture Notes in Artificial Intelligence.
  Springer 2008.
  (Springer) (DBLP)
  

• Diedrich Wolter, Frank Dylla, Stefan Wölfl, Jan Oliver Wallgrün, Lutz Frommberger, Bernhard Nebel and Christian Freksa.
  SailAway: Spatial Cognition in Sea Navigation.
  Künstliche Intelligenz 08 (1), pp. 28-30. 2008.
  (DBLP)
  

• Frank Dylla, Diedrich Wolter, Lutz Frommberger, Christian Freksa, Stefan Wölfl and Bernhard Nebel.
  Qualitative Methoden zur Steuerung von Agenten - SailAway: Raumkognition zur Steuerung von Schiffen.
  Industrie Management 4. 2008.
  (BIB)
  

• Marco Ragni and Stefan Wölfl.
  Reasoning about topological and positional information in dynamic settings.
  In Proceedings of the Twenty-First International FLAIRS Conference (2008), pp. 606-611. 2008.
  (DBLP)
  

• Matthias Westphal and Stefan Wölfl.
  Bipath Consistency Revisited.
  In Proceedings of the ECAI'08 Workshop on Spatial and Temporal Reasoning. Patras, Greece 2008.
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  In the field of qualitative spatial and temporal reasoning combinations of constraint calculi have attracted considerable research interest in recent years. Beside combinations of spatial and temporal calculi, it is an important research topic to develop generic methods for combining calculi dealing with different spatial aspects. The prototypical example is the combination of the region connection calculus RCC8 and the point algebra first discussed by Gerevini and Renz, which allows to represent, and reason about, topological and size information about spatially extended objects. To solve constraints in this calculus, Gerevini and Renz also proposed an algorithm, the bipath consistency algorithm, which allows for deciding consistency of a given constraint network for specific sets of relations combining topology and size. In this article we will compare the "bipath consistency"-based combination method to the standard method, which is to combine calculi by generating a new calculus and applying the standard path consistency method. Gerevini and Renz's calculus combining topological and size information will serve as the running example of such combinations and also as a test case for an empirical analysis.

• Zeno Gantner, Matthias Westphal and Stefan Wölfl.
  GQR - A Fast Reasoner for Binary Qualitative Constraint Calculi.
  In Proceedings of the AAAI'08 Workshop on Spatial and Temporal Reasoning. Chicago, USA 2008.
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  GQR (Generic Qualitative Reasoner) is a solver for binary qualitative constraint networks. GQR takes a calculus description and one or more constraint networks as input, and tries to solve the networks using the path consistency method and (heuristic) backtracking. In contrast to specialized reasoners, it offers reasoning services for different qualitative calculi, which means that these calculi are not hard-coded into the reasoner. Currently, GQR supports arbitrary binary constraint calculi developed for spatial and temporal reasoning, such as calculi from the RCC family, the intersection calculi, Allen's interval algebra, cardinal direction calculi, and calculi from the OPRA family. New calculi can be added to the system by specifications in a simple text format or in an XML file format. The tool is designed and implemented with genericity and extensibility in mind, while preserving efficiency and scalability. The user can choose between different data structures and heuristics, and new ones can be easily added to the object-oriented framework. GQR is free software distributed under the terms of the GNU General Public License.

2007

• Stefan Wölfl, Till Mossakowski and Lutz Schröder.
  Qualitative constraint calculi: Heterogeneous verification of composition tables.
  In Proceedings of the Twentieth International Florida Artificial Intelligence Research Society Conference (FLAIRS 2007), pp. 665-670. AAAI Press 2007.
  

• Diedrich Wolter, Frank Dylla, Lutz Frommberger, Jan Oliver Wallgrün, Bernhard Nebel and Stefan Wölfl.
  Qualitative Spatial Reasoning for Rule Compliant Agent Navigation.
  In Proceedings of the Twentieth International Florida Artificial Intelligence Research Society Conference (FLAIRS 2007), pp. 673-674. AAAI Press 2007.
  

• Frank Dylla, Lutz Frommberger, Jan Oliver Wallgrün, Diedrich Wolter, Berhard Nebel and Stefan Wölfl.
  SailAway: Formalizing navigation rules.
  In Proceedings of the Artificial and Ambient Intelligence Symposium on Spatial Reasoning and Communication (AISB 2007). 2007.
  

2006

• Stefan Wölfl and Till Mossakowski.
  Qualitative Constraint Calculi - Application and Integration, Workshop at KI 2006, Bremen, Germany, June 14, 2006, Workshop Proceedings.
  2006.
  

• Till Mossakowski, Lutz Schroeder and Stefan Wölfl.
  A categorical perspective on qualitative constraint calculi.
  In Qualitative Constraint Calculi - Application and Integration, Workshop at KI 2006. 2006.
  

• Marco Ragni and Stefan Wölfl.
  Temporalizing Cardinal Directions: From Constraint Satisfaction to Planning.
  In Proceedings of the Knowledge Representation Conference (KR 2006). 2006.
  (PDF)
  

2005

• Marco Ragni and Stefan Wölfl.
  Temporalizing Spatial Calculi: On Generalized Neighborhood Graphs.
  In Proceedings of the 28th Annual German Conference on AI (KI 2005), pp. 64-78. 2005.
  (PDF)
  

• Stefan Wölfl and Till Mossakowski.
  CASL specifications of qualitative calculi.
  In Spatial Information Theory: Cognitive and Computational Foundations, Proceedings of COSIT'05, pp. 200-217. 2005.
  

• Stefan Wölfl.
  Events in branching time.
  Studia Logica 79 (2), pp. 255-282. 2005.
  

2004

• Marco Ragni and Stefan Wölfl.
  Branching Allen: Reasoning with Intervals in Branching Time.
  In Spatial Cognition IV: Reasoning, Action, Interaction, International Conference Spatial Cognition 2004, 2004. Proceedings. Springer-Verlag 2004.
  (PDF)
  

• Stefan Wölfl.
  Qualitative action theory: A comparison of the semantics of Alternating-time Temporal Logic and the Kutschera-Belnap approach to agency.
  In J. J. Alferes and J. Leite, Proceedings of the 9th European Conference on Logics in Artificial Intelligence (JELIA 2004). Springer-Verlag 2004.
  (PS.GZ) (PDF)
  

My Erdös number is presumably equal to 4: Stefan Wölfl, Till Mossakowski, George E. Strecker, Marcel Erne, Paul Erdös.