Tommie Meyer

Tommie Meyer is the Co-Director of CAIR and a full professor in Computer Science at the University of Cape Town (UCT). He heads up the Knowledge Representation and Reasoning group at UCT. His research interests are mainly in the area of Knowledge Representation and Reasoning, especially Nonmonotonic Reasoning, Belief Revision, and Description Logics.

He is always looking for good postgraduate students to join the KRR group. If you have an interest in logic-based Artificial Intelligence, please contact him. Details about postgraduate admission in Computer Science at UCT can be found here: http://www.sit.uct.ac.za/sit/postgrad/overview

Link: http://www.tommiemeyer.org.za

Publications

2011

Bergh J, Gerber A, Meyer T, van Zijl L. Path analysis for ontology comprehension. Seventh Australasian Ontology Workshop. 2011.

Abstract BibTex Entry BibTeX Download

n.a.

@misc{462,
  author = {Johann Bergh and Aurona Gerber and Tommie Meyer and Lynette van Zijl},
  title = {Path analysis for ontology comprehension},
  abstract = {n.a.},
  year = {2011},
  journal = {Seventh Australasian Ontology Workshop},
  month = {12/11},
}

Moodley K, Meyer T, Varzinczak I. Root Justifications for Ontology Repair. In: Fifth International Conference on Web Reasoning and Rule Systems. ; 2011.

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RR11-OntologyRepair.pdf

No Abstract

@{32,
  author = {Kody Moodley and Tommie Meyer and Ivan Varzinczak},
  title = {Root Justifications for Ontology Repair},
  abstract = {No Abstract},
  year = {2011},
  journal = {Fifth International Conference on Web Reasoning and Rule Systems},
  pages = {275-280},
}

Nortjé R, Britz K, Meyer T. Bidirectional reachability-based modules. 24th International Workshop on Description Logics (DL 2011). 2011.

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NBM2011.pdf

We introduce an algorithm for MinA extraction in EL based on bidirectional reachability. We obtain a significant reduction in the size of modules extracted at almost no additional cost to that of extracting standard reachability-based modules. Bidirectional modules are related to nested locality modules, but are aimed specifically at MinA extraction and are generally smaller. For acyclic EL TBoxes consisting of only primitive concept inclusions, all MinAs can be extracted without the need for subsumption testing.

@misc{30,
  author = {Riku Nortjé and Katarina Britz and Tommie Meyer},
  title = {Bidirectional reachability-based modules},
  abstract = {We introduce an algorithm for MinA extraction in EL based on bidirectional reachability. We obtain a significant reduction in the size of modules extracted at almost no additional cost to that of extracting standard reachability-based modules. Bidirectional modules are related to nested locality modules, but are aimed specifically at MinA extraction and are generally smaller. For acyclic EL TBoxes consisting of only primitive concept inclusions, all MinAs can be extracted without the need for subsumption testing.},
  year = {2011},
  journal = {24th International Workshop on Description Logics (DL 2011)},
  month = {13/07 - 16/07},
}

Britz K, Meyer T, Varzinczak I. Concept Model Semantics for DL Preferential Reasoning. 24th International Workshop on Description Logics (DL 2011). 2011.

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WP13-BritzEtAl-ConceptModelSemanticsForDLPreferentialReasoning-DL2011.pdf

The preferential and rational consequence relations first studied by Lehmann and colleagues play a central role in non-monotonic reasoning, not least because they provide the foundation for the determination of the important notion of rational closure. Although they can be applied directly to a large variety of logics, these constructions suffer from the limitation that they are largely propositional in nature. One of the main obstacles in moving beyond the propositional case has been the lack of a formal semantics which appropriately generalizes the preferential and ranked models of Lehmann et al. In this paper we propose a semantics to fill that gap for description logics, an important class of decidable fragments of first-order logic. Our semantics replaces the propositional valuations used in the models of Lehmann et al. with structures we refer to as concept models. We prove representation results for the description logic ALC for both preferential and rational consequence relations. We argue that our semantics paves the way for extending preferential and rational consequence, and therefore also rational closure, to a whole class of logics that have a semantics defined in terms of first-order relational structures.

@misc{28,
  author = {Katarina Britz and Tommie Meyer and Ivan Varzinczak},
  title = {Concept Model Semantics for DL Preferential Reasoning},
  abstract = {The preferential and rational consequence relations first studied by Lehmann and colleagues play a central role in non-monotonic reasoning, not least because they provide the foundation for the determination of the important notion of rational closure. Although they can be applied directly to a large variety of logics, these constructions suffer from the limitation that they are largely propositional in nature. One of the main obstacles in moving beyond the propositional case has been the lack of a formal semantics which appropriately generalizes the preferential and ranked models of Lehmann et al. In this paper we propose a semantics to fill that gap for description logics, an important class of decidable fragments of first-order logic. Our semantics replaces the propositional valuations used in the models of Lehmann et al. with structures we refer to as concept models. We prove representation results for the description logic ALC for both preferential and rational consequence relations. We argue that our semantics paves the way for extending preferential and rational consequence, and therefore also rational closure, to a whole class of logics that have a semantics defined in terms of first-order relational structures.},
  year = {2011},
  journal = {24th International Workshop on Description Logics (DL 2011)},
  month = {13/07 - 16/07},
}

Britz K, Meyer T, Varzinczak I. Semantic Foundation for Preferential Description Logics. In: Proceedings of the 24th Australasian Joint Conference on Artificial Intelligence. ; 2011.

Abstract BibTex Entry BibTeX Download PDF

CP10-BritzEtAl-SemanticFoundationForPreferentialDL-AI2011.pdf

Description logics are a well-established family of knowledge representation formalisms in Artificial Intelligence. Enriching description logics with non-monotonic reasoning capabilities, especially preferential reasoning as developed by Lehmann and colleagues in the 90's, would therefore constitute a natural extension of such KR formalisms. Nevertheless, there is at present no generally accepted semantics, with corresponding syntactic characterization, for preferential consequence in description logics. In this paper we fill this gap by providing a natural and intuitive semantics for defeasible subsumption in the description logic ALC. Our semantics replaces the propositional valuations used in the models of Lehmann et al. with structures we refer to as concept models. We present representation results for the description logic ALC for both preferential and rational consequence relations. We argue that our semantics paves the way for extending preferential and rational consequence, and therefore also rational closure, to a whole class of logics that have a semantics defined in terms of first-order relational structures.

@{27,
  author = {Katarina Britz and Tommie Meyer and Ivan Varzinczak},
  title = {Semantic Foundation for Preferential Description Logics},
  abstract = {Description logics are a well-established family of knowledge representation formalisms in Artificial Intelligence. Enriching description logics with non-monotonic reasoning capabilities, especially preferential reasoning as developed by Lehmann and colleagues in the 90&#039;s, would therefore constitute a natural extension of such KR formalisms. Nevertheless, there is at present no generally accepted semantics, with corresponding syntactic characterization, for preferential consequence in description logics. In this paper we fill this gap by providing a natural and intuitive semantics for defeasible subsumption in the description logic ALC. Our semantics replaces the propositional valuations used in the models of Lehmann et al. with structures we refer to as concept models. We present representation results for the description logic ALC for both preferential and rational consequence relations. We argue that our semantics paves the way for extending preferential and rational consequence, and therefore also rational closure, to a whole class of logics that have a semantics defined in terms of first-order relational structures.},
  year = {2011},
  journal = {Proceedings of the 24th Australasian Joint Conference on Artificial Intelligence},
  pages = {491-500},
}

Meyer T, Varzinczak I. A Logic-Based Perspective on Agent Reconfiguration: Preliminary Report. In: IEEE Africon. ; 2011.

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CP09-MeyerVarzinczak-LogicBasedAgentReconfiguration-Africon2011.pdf

We investigate the problem of maintaining and reasoning with different configurations of a logic-based agent. Given specific contexts, there may be several possible usual configurations that the agent's knowledge base can be in, and that one may want to access at different times. This can happen due to foreseeable exceptional situations one has to cater for, or different environments in which the agent may have to operate, or simply due to upgrades of the agent's initial configuration. In all these cases, there is a need for a system capable of managing possibly conflicting versions of the knowledge base and allowing the agent to switch between any two given configurations at run time. Building on Franconi et al.'s framework for propositional knowledge base versioning, here we establish the logical foundations for a general semantic-based architecture of such a system. Central to our approach is the notion of logical difference, which allows us to determine the essential pieces of information on which two given configurations of an agent differ.

@{26,
  author = {Tommie Meyer and Ivan Varzinczak},
  title = {A Logic-Based Perspective on Agent Reconfiguration: Preliminary Report},
  abstract = {We investigate the problem of maintaining and reasoning with different configurations of a logic-based agent. Given specific contexts, there may be several possible usual configurations that the agent&#039;s knowledge base can be in, and that one may want to access at different times. This can happen due to foreseeable exceptional situations one has to cater for, or different environments in which the agent may have to operate, or simply due to upgrades of the agent&#039;s initial configuration. In all these cases, there is a need for a system capable of managing possibly conflicting versions of the knowledge base and allowing the agent to switch between any two given configurations at run time. Building on Franconi et al.&#039;s framework for propositional knowledge base versioning, here we establish the logical foundations for a general semantic-based architecture of such a system. Central to our approach is the notion of logical difference, which allows us to determine the essential pieces of information on which two given configurations of an agent differ.},
  year = {2011},
  journal = {IEEE Africon},
}

Booth R, Meyer T, Varzinczak I, Wassermann R. On the Link between Partial Meet, Kernel, and Infra Contraction and its Application to Horn Logic. Journal of Artificial Intelligence Research. 2011;42.

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JA04-BoothEtAl-HornContraction-JAIR2011.pdf

Standard belief change assumes an underlying logic containing full classical propositional logic. However, there are good reasons for considering belief change in less expressive logics as well. In this paper we build on recent investigations by Delgrande on contraction for Horn logic. We show that the standard basic form of contraction, partial meet, is too strong in the Horn case. This result stands in contrast to Delgrande's conjecture that orderly maxichoice is the appropriate form of contraction for Horn logic. We then define a more appropriate notion of basic contraction for the Horn case, influenced by the convexity property holding for full propositional logic and which we refer to as infra contraction. The main contribution of this work is a result which shows that the construction method for Horn contraction for belief sets based on our infra remainder sets corresponds exactly to Hansson's classical kernel contraction for belief sets, when restricted to Horn logic. This result is obtained via a detour through contraction for belief bases. We prove that kernel contraction for belief bases produces precisely the same results as the belief base version of infra contraction. The use of belief bases to obtain this result provides evidence for the conjecture that Horn belief change is best viewed as a 'hybrid' version of belief set change and belief base change. One of the consequences of the link with base contraction is the provision of a representation result for Horn contraction for belief sets in which a version of the Core-retainment postulate features.

@article{24,
  author = {Richard Booth and Tommie Meyer and Ivan Varzinczak and R. Wassermann},
  title = {On the Link between Partial Meet, Kernel, and Infra Contraction and its Application to Horn Logic},
  abstract = {Standard belief change assumes an underlying logic containing full classical propositional logic. However, there are good reasons for considering belief change in less expressive logics as well. In this paper we build on recent investigations by Delgrande on contraction for Horn logic. We show that the standard basic form of contraction, partial meet, is too strong in the Horn case. This result stands in contrast to Delgrande&#039;s conjecture that orderly maxichoice is the appropriate form of contraction for Horn logic. We then define a more appropriate notion of basic contraction for the Horn case, influenced by the convexity property holding for full propositional logic and which we refer to as infra contraction. The main contribution of this work is a result which shows that the construction method for Horn contraction for belief sets based on our infra remainder sets corresponds exactly to Hansson&#039;s classical kernel contraction for belief sets, when restricted to Horn logic. This result is obtained via a detour through contraction for belief bases. We prove that kernel contraction for belief bases produces precisely the same results as the belief base version of infra contraction. The use of belief bases to obtain this result provides evidence for the conjecture that Horn belief change is best viewed as a &#039;hybrid&#039; version of belief set change and belief base change. One of the consequences of the link with base contraction is the provision of a representation result for Horn contraction for belief sets in which a version of the Core-retainment postulate features.},
  year = {2011},
  journal = {Journal of Artificial Intelligence Research},
  volume = {42},
  pages = {31-53},
}

Britz K, Meyer T, Varzinczak I. Preferential Reasoning for Modal Logic. Electronic Notes in Theoretical Computer Science. 2011;278.

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JA06-BritzEtAl-PreferentialReasoningForModalLogic-ENTCS2011.pdf

Modal logic is the foundation for a versatile and well-established class of knowledge representation formalisms in artificial intelligence. Enriching modal logics with non-monotonic reasoning capabilities such as preferential reasoning as developed by Lehmann and colleagues would therefore constitute a natural extension of such KR formalisms. Nevertheless, there is at present no generally accepted semantics, with corresponding syntactic characterization, for preferential consequence in modal logics. In this paper we fill this gap by providing a natural and intuitive semantics for preferential and rational modal consequence. We do so by placing a preference order on possible worlds indexed by Kripke models they belong to. We also prove representation results for both preferential and rational consequence, which paves the way for effective decision procedures for modal preferential reasoning. We then illustrate applications of our constructions to modal logics widely used in AI, notably in the contexts of reasoning about actions, knowledge and beliefs. We argue that our semantics constitutes the foundation on which to explore preferential reasoning in modal logics in general.

@article{23,
  author = {Katarina Britz and Tommie Meyer and Ivan Varzinczak},
  title = {Preferential Reasoning for Modal Logic},
  abstract = {Modal logic is the foundation for a versatile and well-established class of knowledge representation formalisms in artificial intelligence. Enriching modal logics with non-monotonic reasoning capabilities such as preferential reasoning as developed by Lehmann and colleagues would therefore constitute a natural extension of such KR formalisms. Nevertheless, there is at present no generally accepted semantics, with corresponding syntactic characterization, for preferential consequence in modal logics. In this paper we fill this gap by providing a natural and intuitive semantics for preferential and rational modal consequence. We do so by placing a preference order on possible worlds indexed by Kripke models they belong to. We also prove representation results for both preferential and rational consequence, which paves the way for effective decision procedures for modal preferential reasoning. We then illustrate applications of our constructions to modal logics widely used in AI, notably in the contexts of reasoning about actions, knowledge and beliefs. We argue that our semantics constitutes the foundation on which to explore preferential reasoning in modal logics in general.},
  year = {2011},
  journal = {Electronic Notes in Theoretical Computer Science},
  volume = {278},
  pages = {55-69},
}

Booth R, Meyer T. Belief Change. In: Logic and Philosophy Today, Vol. 1, Studies in Logic, Vol. 29. College Publications; 2011. www.collegepublications.co.uk/logic/mlf/?00017.

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Booth_Meyer.pdf

In this paper we present a brief overview of belief change, a research area concerned with the question of how a rational agent ought to change its mind in the face of new, possibly conflicting, information. We limit ourselves to logic-based belief change, with a particular emphasis on classical propositional logic as the underlying logic in which beliefs are to be represented. Our intention is to provide the reader with a basic introduction to the work done in this area over the past 30 years. In doing so we hope to sketch the main historical results, provide appropriate pointers to further references, and discuss some current developments. We trust that this will spur on the interested reader to learn more about the topic, and perhaps to join us in the further development of this exciting field of research.

@inbook{17,
  author = {Richard Booth and Tommie Meyer},
  title = {Belief Change},
  abstract = {In this paper we present a brief overview of belief change, a research area concerned with the question of how a rational agent ought to change its mind in the face of new, possibly conflicting, information. We limit ourselves to logic-based belief change, with a particular emphasis on classical propositional logic as the underlying logic in which beliefs are to be represented. Our intention is to provide the reader with a basic introduction to the work done in this area over the past 30 years. In doing so we hope to sketch the main historical results, provide appropriate pointers to further references, and discuss some current developments. We trust that this will spur on the interested reader to learn more about the topic, and perhaps to join us in the further development of this exciting field of research.},
  year = {2011},
  journal = {Logic and Philosophy Today, Vol. 1, Studies in Logic, Vol. 29},
  pages = {385-422},
  publisher = {College Publications},
  url = {www.collegepublications.co.uk/logic/mlf/?00017},
}