Publications on Defeasible Logic
- Grigoris Antoniou, David Billington, Guido Governatori, and
Michael J. Maher.
-
On the modeling and analysis of
regulations.
In Proceedings of the Australian Conference Information Systems,
pages 20-29, 1999.
Abstract:Regulations are a wide-spread and important part of
government and business. They codify how products must be made and processes
should be performed. Such regulations can be difficult to understand and
apply. In an environment of growing complexity of, and change in, regulation,
automated support for reasoning with regulations is becoming increasingly
necessary. In this paper we report on ongoing work which aims at providing
automated support for the drafting and use of regulations using logic
modelling techniques. We highlight the support that can be provided by logic
modelling, describe the technical foundation of our project, and report on
the status of the project and the next steps.
 
- Grigoris Antoniou, David Billington, Guido Governatori,
and Michael J. Maher.
-
A flexible framework for defeasible
logics.
In Proc. American National Conference on Artificial Intelligence
(AAAI-2000), pages 401-405, Menlo Park, CA, 2000. AAAI/MIT Press,
Copyright © 2000 AAAI, American Association for Artificial
Intelligence.
Abstract:Logics for knowledge representation suffer from
over-specialization: while each logic may provide an ideal representation
formalism for some problems, it is less than optimal for others. A solution
to this problem is to choose from several logics and, when necessary, combine
the representations. In general, such an approach results in a very difficult
problem of combination. However, if we can choose the logics from a uniform
framework then the problem of combining them is greatly simplified. In this
paper, we develop such a framework for defeasible logics. It supports all
defeasible logics that satisfy a strong negation principle. We use logic
meta-programs as the basis for the framework.
 
- Grigoris Antoniou, David Billington, Guido Governatori, and
Michael J. Maher.
-
A flexible framework for defeasible logics.
In Proceeding of the 9th Workshop on Non-Monotonic Reasoning,
2000.
Abstract:Logics for knowledge representation suffer from
over-specialization: while each logic may provide an ideal representation
formalism for some problems, it is less than optimal for others. A solution
to this problem is to choose from several logics and, when necessary, combine
the representations. In general, such an approach results in a very difficult
problem of combination. However, if we can choose the logics from a uniform
framework then the problem of combining them is greatly simplified. In this
paper, we develop such a framework for defeasible logics. It supports all
defeasible logics that satisfy a strong negation principle. We use logic
meta-programs as the basis for the framework.
 
- Grigoris Antoniou, David Billington, Guido Governatori, and
Michael J. Maher.
-
Representation results for defeasible logic.
ACM Transactions on Computational Logic, 2 no. 2 pp. 255-287,
April 2001., Copyright
© 2001 ACM.
Abstract:The importance of transformations and normal forms in
logic programming, and generally in computer science, is well documented.
This paper investigates transformations and normal forms in the context of
Defeasible Logic, a simple but efficient formalism for nonmonotonic reasoning
based on rules and priorities. The transformations described in this paper
have two main benefits: on one hand they can be used as a theoretical tool
that leads to a deeper understanding of the formalism, and on the other hand
they have been used in the development of an efficient implementation of
defeasible logic.
 
- Grigoris Antoniou, David Billington, Guido
Governatori and Micheal J. Maher.
- Embedding
Defeasible Logic into Logic Programming
Theory and Practice of Logic Programming, 6, 6, pp
803-835. Copyright
© Cambridge University Press.
Abstract: Defeasible reasoning is a simple but efficient
approach to nonmonotonic reasoning that has recently attracted
considerable interest and that has found various
applications. Defeasible logic and its variants are an important
family of defeasible reasoning methods. So far no relationship has
been established between defeasible logic and mainstream
nonmonotonic reasoning approaches.
In this paper we establish close links to known semantics of logic
programs. In particular, we give a translation of a defeasible
theory D into a meta-program P(D). We show that under a
condition of decisiveness, the defeasible consequences of D
correspond exactly to the sceptical conclusions of P(D) under the
stable model semantics. Without decisiveness, the result holds only
in one direction (all defeasible consequences of D are included in
all stable models of P(D)). If we wish a complete embedding for
the general case, we need to use the Kunen semantics of P(D),
instead.
 
- Grigoris Antoniou, David Billington, Guido
Governatori, Michael J. Maher, and Andrew Rock.
-
A family of defeasible reasoning logics and
its implementation.
In Werner Horn, editor, ECAI 2000. Proceedings of the 14th European
Conference on Artificial Intelligence, pages 459-463, Amsterdam, 2000.
IOS Press.
Abstract:Defeasible reasoning is a direction in nonmonotonic
reasoning that is based on the use of rules that may be defeated by other
rules. It is a simple, but often more efficient approach than other
nonmonotonic reasoning systems. This paper presents a family of defeasible
reasoning formalisms built around Nute's defeasible logic. We describe the
motivations of these formalisms and derive some basic properties and
interrelationships. We also describe a query answering system that supports
these formalisms and is available on the World Wide Web.
 
- Grigoris Antoniou, Nikos Dimaresis, and Guido
Governatori.
-
A
system for modal and deontic defeasible reasoning.
In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint
Conference on Artificial Intelligence, AI 2007,
LNAI 4830, pages 609-613. Springer, 2007.
Copyright © 2007 Springer.
Abstract:
Defeasible reasoning is a well-established nonmonotonic reasoning approach that
has recently been combined with semantic web technologies. This paper describes
modal and deontic extensions of defeasible logic, motivated by potential
applications for modelling multi-agent systems and policies. It describes a
logic metaprogram that captures the underlying intuitions, and outlines an
implemented system.
- Grigoris Antoniou, Michael J. Maher, David Billington, and
Guido Governatori.
-
Comparison of sceptical naf-free logic
programming approaches.
In M. Gelfond, N. Leone, and G. Pfeifer, editors, Logic Programming and
Non-monotonic Reasoning, volume 1730 of LNAI, pages 347-356,
Berlin, 1999. Springer-Verlag, Copyright © 1999 Springer-Verlag.
Abstract:Recently there has been increased interest in logic
programming-based default reasoning approaches which are not using
negation-as-failure in their object language. Instead, default reasoning is
modelled by rules and a priority relation among them. Historically the first
logic in this class was Defeasible Logic. In this paer we will study its
relationship to other approaches which also rely on the idea of using logic
rules and priorities. In particular we will study sceptical LPwNF, courteous
logic programs, and priority logic.
 
- Nick Bassiliades, Grigoris Antoniou and Guido
Governatori.
- Proof
Explanation in the DR-DEVICE System. In M. Marchiori, J.Z.Pan and C. de
Sainte Marie (eds) Web Reasoning and Rule Systems, LNCS 4524, pages
249-258. Springer, Berlin, 2007. Copyright © 2007 Springer.
Abstract:
Trust is a vital feature for the Semantic Web: If users (humans and agents)
are to use and integrate system answers, they must trust them. Thus, systems
should be able to explain their actions, sources, and beliefs, and this issue
is the topic of the proof layer in the design of the Semantic Web. This paper
presents the design of a system for proof explanation on the Semantic Web,
based on defeasible reasoning. The basis of this work is the DR-DEVICE system
that is extended to handle proofs. A critical aspect is the representation of
proofs in an XML language, which is achieved by a RuleML language extension.
 
- David Billington, Grigoris Antoniou, Guido Governatori, and
Michael J. Maher.
-
Revising nonmonotonic belief sets: The case
of defeasible logic.
In Wolfram Burgard, Thomas Christaller, and Armin B. Cremers, editors,
KI-99: Advances in Artificial Intelligence, volume 1701 of
LNAI, pages 101-112, Berlin, 1999. Springer-Verlag, Copyright © 1999
Springer-Verlag.
Abstract:The revision and transformation of knowledge is widely
recognized as a key issue in knowledge representation and reasoning. Reasons
for the importance of this topic are the fact that intelligent systems are
gradually developed and refined, and that often the environment of an
intelligent system is not static but changes over time. Traditionally belief
revision has been concerned with revising first order theories. Nonmonotonic
reasoning provides rigorous techniques for reasoning with incomplete
information. Until recently the dynamics of nonmonotonic reasoning approaches
has attracted little attention. This paper studies the dynamics of defeasible
logic, a simple and efficient form of nonmonotonic reasoning based on
defeasible rules and priorities. We define revision and contraction
operators, propose postulates motivated by the form or the intuition of the
AGM postulates for classical belief revision, and verify that the operators
satisfy the postulates.
 
- David Billington, Grigoris Antoniou, Guido Governatori,
and Michael J. Maher.
-
An inclusion theorem for defeasible logic.
ACM Transactions in Computational Logic.
Abstract: Defeasible reasoning is a computationally simple
nonmonotonic reasoning approach that has attracted significant theoretical
and practical attention. It comprises a family of logics that capture
different intuitions, among them ambiguity propagation versus ambiguity
blocking, and the adoption or rejection of team defeat. This paper provides a
compact presentation of the defeasible logic variants, and derives an
Inclusion Theorem which shows that different notions of provability in
defeasible logic form a chain of levels of proof.
 
- Guido Boella, Guido Governatori, Joris Hulstijn,
Régis Riveret, Antonino Rotolo, and Leendert van der Torre.
-
Time and
defeasibility in FIPA ACL semantics.
In 2008 IEEE/WIC/ACM International Conference on Web Intelligence and
Intelligent Agent Technology, pages 634-637. IEEE Press,
2008, Copyright ©
2008 IEEE.
Abstract: Inferences about communicative actions are often
conditional, non-monotonic, and involve the issue of time. Most agent
communication languages, however, ignore these issues, due to the difficulty
to combine them in a single formalism. This paper addresses such issues in
defeasible logic, and illustrates how to express a semantics for ACLs in
order to make non-monotonic inferences on the basis of communicative actions.
 
-
Guido Boella, Guido Governatori, Joris Hulstijn, Régis Riveret,
Antonino Rotolo and Leemndert van der Torre.
-
FIPA Communicative Acts in Defeasible Logic.
In Alankar Karol, Pavlos Peppas and Mary-Anne Williams, editor,
Seventh IJCAI International Workshop on Nonmonotonic Reasoning,
Action and Change (NRAC'07), Hyderabad, India, 7-8 January, 2007.
Abstract: In agent communication languages, the inferences
that can be made on the basis of a communicative action are inherently
conditional, and non-monotonic. For example, a proposal only leads to
a commitment, on the condition that it is accepted. And in a
persuasion dialogue, assertions may later be retracted. In this paper
we therefore present a defeasible logic that can be used to express a
semantics for agent communication languages, and to efficiently make
inferences on the basis of communicative actions. The logic is
non-monotonic, allows nested rules and mental attitudes as the content
of communicative actions, and has an explicit way of expressing
persistence over time. Moreover, it expresses that mental attitudes
are publicly attributed to agents playing roles in the dialogue. To
illustrate the usefulness of the logic, we reformalize the meta-theory
underlying the FIPA semantics for agent communication, focusing on
inform and propose. We show how composed speech acts can be
formalized, and extend the semantics with an account of persuasion.
- Guido Boella, Guido Governatori, Antonino Rotolo, and
Leendert van der Torre.
-
Lex minus dixit quam voluit, lex magis dixit quam voluit: A formal
study on legal compliance and interpretation.
In P. Casanovas, U. Pagallo, G. Ajani, and G. Sartor, editors, AI
approaches to the complexity of legal systems, LNAI, Berlin, 2010.
Springer, Copyright © 2010 Springer.
Abstract: This paper argues in favour of the necessity of
dynamically restricting and expanding the applicability of norms regulating
computer systems like multiagent systems, in situations where the compliance
to the norm does not achieve the purpose of the norm. We propose a logical
framework which distinguishes between constitutive and regulative norms and
captures the norm change power and at the same time the limitations of the
judicial system in dynamically revising the set of constitutive rules
defining the concepts on which the applicability of norms is based. In
particular, the framework is used to reconstruct some interpretive arguments
described in legal theory such as those corresponding to the Roman maxims
lex minus dixit quam voluit and lex magis dixit quam voluit.
The logical framework is based on an extension of defeasible logic.
 
- Mehdi Dastani, Guido Governatori, Antonio Rotolo, Insu Song and
Leendert van der Torre.
-
Contextual Deliberation of Cognitive Agents in Defeasible Logic. In
6th International Conference on Autonomous Agents and Multi-Agent
Systems. ACM Press, New York. Copyright
© 2007 ACM.
Abstract: This article extends Defeasible
Logic to deal with the contextual deliberation process of cognitive agents.
First, we introduce meta-rules to reason with rules. Meta-rules are rules that
have as a consequent rules for motivational components, such as obligations,
intentions and desires. In other words, they include nested rules. Second, we
introduce explicit preferences among rules. They deal with complex structures
where nested rules can be involved.
 
- Mehdi Dastani, Guido Governatori, Antonino Rotolo,
Insu Song, and Leendert van der Torre.
-
Contextual
agent deliberation in defeasible logic.
In Aditya Ghose and Guido Governatori, editors, 10 Pacific Rim
International Workshop on Multi-Agents, LNAI 5044. Springer, 2008
Copyright © 2008 Springer.
Abstract: This article extends Defeasible Logic to deal with the
contextual deliberation process of cognitive agents. First, we introduce
meta-rules to reason with rules. Meta-rules are rules that have as a
consequent rules for motivational components, such as obligations, intentions
and desires. In other words, they include nested rules. Second, we introduce
explicit preferences among rules. They deal with complex structures where
nested rules can be involved.
- Mehdi Dastani, Guido Governatori, Antonino Rotolo and
Leendert van der Torre
-
Preferences of Agents in Defeasible Logic.
In S. Zhang and R. Jarvis, editors, Australian Joint Conference on Artificial Intelligence, AI 2005, pages 695-704. LNCS 3809, Springer, Berlin,
2005, Copyright ©
2005 Springer.
Abstract:
We are interested in programming languages for cognitive agents with
preferences. We define rule-based agent theories and inference
procedures in defeasible logic, and in this setting we discuss
patterns of agent behavior called agent types.
 
- Mehdi Dastani, Guido Governatori, Antonino Rotolo and
Leendert van der Torr
-
Programming Cognitive Agents in Defeasible Logic.
In G. Sutcliffe and A. Voronkov, editors, Logic Programming and Automated Reasoning. LPAR 2005, pages 621-635. LNCS 3835, Springer, Berlin,
2005, Copyright ©
2005 Springer.
Abstract:
Defeasible Logic is extended to programming languages for
cognitive agents with preferences and actions for planning. We
define rule-based agent theories that contain preferences and
actions, together with inference procedures. We discuss patterns of
agent types in this setting. Finally, we illustrate the
language by an example of an agent reasoning about web-services.
 
- Jenny Eriksson Lundström, Guido Governatori,
Subhasis Thakur, and Vineet Padmanabhan.
-
An
asymmetric protocol for argumentation games in defeasible logic.
In Aditya Ghose and Guido Governatori, editors, 10 Pacific Rim
International Workshop on Multi-Agents, LNAI 5044. Springer, 2008
Copyright © 2008 Springer.
Abstract: Agent interactions where the agents hold conflicting
goals could be modelled as adversarial argumentation games. In many real-life
situations (e.g., criminal litigation, consumer legislation), due to ethical,
moral or other principles governing interaction, the burden of proof, i.e.,
which party is to lose if the evidence is balanced, is a
priori fixed to one of the parties. Analogously, when resolving disputes in
a heterogeneous agent-system the unequal importance of different agents for
carrying out the overall system goal need to be accounted for. In this paper
we present an asymmetric protocol for an adversarial argumentation game in
Defeasible Logic, suggesting Defeasible Logic as a general representation
formalism for argumentation games modelling agent interactions.
- Guido Governatori.
-
Defeasible description logic.
In Grigoris Antoniou and Harold Boley, editors, Rules and Rule Markup
Languages for the Semantic Web: Third International Workshop, RuleML
2004, number 3323 in LNCS, pages 98-112, Berlin, 8 November 2004.
Springer-Verlag Copyright © 2004, Springer. The original
pubblication is available at www.springerlink.com
Abstract:We propose to extend description logic with defeasible
rules, and to use the inferential mechanism of defeasible logic to reason
with description logic constructors.
 
- Guido Governatori.
-
Representing business contracts in RuleML.
International Journal of Cooperative Information Systems, 14
no. 2-3, June-September 2005, pp. 181-216.
Abstract:This paper presents an approach for the specification
and implementation of translating contracts from a human-oriented form into
an executable representation for monitoring. This will be done in the setting
of RuleML. The task of monitoring contract execution and performance
requires a logical account of deontic and defeasible aspects of legal
language; currently such aspects are not covered by RuleML; accordingly we
show how to extend it to cover such notions. From its logical form, the
contract will be thus transformed into a machine readable rule notation and
eventually implemented as executable semantics via any mark-up languages
depending on the client's preference, for contract monitoring purposes.
 
- Guido Governatori.
-
On
the relationship between Carneades and defeasible logic.
In Tom van Engers, editor, Proceedings of the 13th International
Conference on Artificial Intelligence and Law (ICAIL 2011). ACM Press,
2011. Copyrigth © 2011 ACM Press.
Abstract: We study the formal relationships between the
inferential aspects of Carneades (a general argumentation framework) and
Defeasible Logic. The outcome of the investigation is that the current proof
standards proposed in the Carneades framework correspond to some variants of
Defeasible Logic.
 
- Guido Governatori, Marlon Dumas, Arthur H.M. ter Hofstede,
and Phillipa Oaks.
-
A formal approach to protocols and strategies
for (legal) negotiation.
In Henry Prakken, editor, Procedings of the 8th International Conference
on Artificial Intelligence and Law, pages 168-177. IAAIL, ACM Press,
2001, Copyright ©
2001 ACM.
Abstract:We propose a formal and executable framework for
expressing protocols and strategies for automated (legal) negotiation. In
this framework a party involved in a negotiation is represented through a
software agent composed of four modules: (i) a communication module which
manages the interaction with the other agents; (ii) a control module; (iii) a
reasoning module specified as a defeasible theory; and (iv) a knowledge base
which bridges the control and the reasoning modules, while keeping track of
past decisions and interactions. The choice of defeasible logic is justified
against a set of desirable criteria for negotiation automation languages.
Moreover, the suitability of the framework is illustrated through two case
studies.
 
- Guido Governatori, Joris Hulstijn, Régis
Riveret, and Antonino Rotolo.
-
Characterising deadlines in temporal modal defeasible logic.
In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint
Conference on Artificial Intelligence, AI 2007,
LNAI 4830, pages 486-496. Springer, 2007.
Copyright © 2007 Springer.
Abstract: We provide a conceptual analysis of several kinds of
deadlines, represented in Temporal Modal Defeasible Logic. The paper presents
a typology of deadlines, based on the following parameters: deontic operator,
maintenance or achievement, presence or absence of sanctions, and persistence
after the deadline. The deadline types are illustrated by a set of examples.
- Guido Governatori and Michael J. Maher.
-
An argumentation-theoretic characterization
of defeasible logic.
In Werner Horn, editor, ECAI 2000. Proceedings of the 14th European
Conference on Artificial Intelligence, pages 469-474, Amsterdam, 2000.
IOS Press.
Abstract:Defeasible logic is an efficient non-monotonic logic
that is defined only proof-theoretically. It has potential application in
some legal domains. We present here an argumentation semantics for defeasible
logic that will be useful in these applications. Our development differs at
several points from existing argumentation frameworks since there are several
features of defeasible logic that have not been addressed in the literature.
 
- Guido Governatori, Michael J. Maher, Grigoris
Antoniou, and David Billington.
-
Argumentation semantics for defeasible
logics.
In Riichiro Mizoguchi and John Slaney, editors, PRICAI 2000: Topics in
Artificial Intelligence, volume 1886 of LNAI, pages 27-37,
Berlin, 2000. Springer-Verlag, Copyright © 2000
Springer-Verlag.
Abstract:Defeasible logic is an efficient non-monotonic logic
that is defined only proof-theoretically. It has potential application in
some legal domains. We present here argumentation semantics for variants of
defeasible logic that will be useful in these applications.
 
- Guido Governatori, Michael J. Maher, David
Billington, and Grigoris Antoniou.
-
Argumentation semantics for defeasible logics.
Journal of Logic and Computation, 14, no. 5,
pp. 675-702, 2004.
Copyright ©
2004 Oxford University Press.
Abstract:Defeasible reasoning is a simple but efficient
rule-based approach to nonmonotonic reasoning. It has powerful
implementations and shows promise to be applied in the areas of legal
reasoning and the modeling of business rules. This paper establishes
significant links between defeasible reasoning and argumentation. In
particular, Dung-like argumentation semantics is provided for two key
defeasible logics, of which one is ambiguity propagating and the other
ambiguity blocking. There are several reasons for the significance of this
work: (a) establishing links between formal systems leads to a better
understanding and cross-fertilization, in particular our work sheds light on
the argumentation-theoretic features of defeasible logic; (b) we provide the
first ambiguity blocking Dung-like argumentation system; (c) defeasible
reasoning may provide an efficient implementation platform for systems of
argumentation; and (d) argumentation-based semantics support a deeper
understanding of defeasible reasoning, especially in the context of the
intended applications.
 
- Guido Governatori, Francesco Olivieri, Simone
Scannapieco, and Matteo Cristani.
-
Superiority based revision of defeasible theories.
In Mike Dean, John Hall, Antonino Rotolo, and Said Tabet, editors, RuleML
2010: 4th International Web Rule Symposium, number 6403 in LNCS, pages
104-118, Berlin, 2010. Springer. Copyrigth © 2010 Springer.
Abstract: We propose a systematic investigation on how to modify
a preference relation in a defeasible logic theory to change the conclusions
of the theory itself. We argue that the approach we adopt is applicable to
legal reasoning, where users, in general, cannot change facts and rules, but
can propose their preferences about the relative strength of the rules. We
provide a comprehensive study of the possible combinatorial cases and we
identify and analyse the cases where the revision process is successful.
 
- Guido Governatori and Vineet Padmanabhan.
-
A defeasible logic of policy-based
intention.
In Tamás D. Gedeon and Lance Chun Che Fung, editors, AI 2003:
Advances in Artificial Intelligence, volume 2903 of LNAI, pages
414-426, Springer-Verlag, Berlin, 2003. Copyright © 2003 Springer-Verlag.
Abstract:Most of the theories on formalising intention interpret
it as a unary modal operator in Kripkean semantics, which gives it a
monotonic look. We argue that policy-based intentions exhibit
non-monotonic behaviour which could be captured through a non-monotonic
system like defeasible logic. To this end we outline a defeasible logic of
intention. The proposed technique alleviates most of the problems related to
logical omniscience. The proof theory given shows how our approach helps in
the maintenance of intention-consistency in agent systems like BDI.
 
- Guido Governatori, Vineet Padmanabhan, and
Antonino Rotolo.
-
Rule-based agents in temporalised defeasible logic. In Qiang
Yang and Geoff Webb, editors, Ninth Pacific Rim International
Conference on Artificial Intelligence, LNAI 4099, pages 31-40,
Guilin, 7-11 August 2006. Springer, Copyright © 2006
Springer.
Abstract:This paper provides a framework
based on temporal defeasible logic to reason about deliberative
rule-based cognitive agents. Compared to previous works in this
area our framework has the advantage that it can reason about
temporal rules. We show that for rule-based cognitive agents
deliberation is more than just deriving conclusions in terms of
their mental components. Our paper is an extension of [5,6]
in the area of cognitive agent programming.
 
- Guido Governatori, Vineet Padmanabhan, Antonino
Rotolo, and Abdul Sattar.
-
A defeasible
logic for modelling policy-based intentions and motivational attitudes.
Logic Journal of the IGPL, 17(3), 2009. Copyright © 2009 Oxford University
Press.
Abstract: In this paper we show how defeasible logic
could formally account for the non-monotonic properties involved in
motivational attitudes like intention and obligation. Usually,
normal modal operators are used to represent such attitudes wherein
classical logical consequence and the rule of necessitation comes into play
i.e., $\vdash A / \vdash \Box A$, that is from $\vdash A$ derive $\vdash\Box
A$. This means that such formalisms are affected by the Logical
Omniscience problem. We show that policy-based intentions exhibit
non-monotonic behaviour which could be captured through a non-monotonic
system like defeasible logic. To this end we outline a defeasible logic of
intention that specifies how modalities can be introduced and manipulated in
a non-monotonic setting without giving rise to the problem of logical
omniscience. In a similar way we show how to add deontic modalities
defeasibly and how to integrate them with other motivational attitudes like
beliefs and goals. Finally we show that the basic aspect of the BOID
architecture is captured by this extended framework.
 
- Guido Governatori, Monica Palmirani, Régis Riveret,
Antonino Rotolo and Giovanni Sartor.
-
Norm Modifications in Defeasible Logic.
In Marie-Francine Moens, editor, Jurix'05: The Eighteenth Annual
Conference, pages 13-22. IOS Press, Amsterdam 2005.
Abstract:
This paper proposes a framework based on Defeasible Logic (DL) to
reason about normative modifications. We show how to express them in
DL and how the logic deals with conflicts between temporalised
normative modifications. Some comments will be given with regard to
the phenomenon of retroactivity.
 
- Guido Governatori, and Duy Hoang Pham
- DR-CONTRACT: An Architecture for e-Contracts in Defeasible Logic
In Claudio Bartolini, Guido Governatori, and Zoran Milosevic (eds).
Proceedings on the 2nd EDOC Workshop on Contract Architecures and
Languages (CoALa 2005). Enschede, NL, 20 September 2005.
IEEE Press.
Abstract:In this paper we present an architecture to
represent and reason on e-Contracts based on the DR-device
architecture supplemented with a deontic defeasible logic of
violation. We motivate the choice for the logic and we show how to
extend RuleML to capture the notions relevant to describe
e-contracts for a monitoring perspective in Defeasible Logic.
 
- Guido Governatori and Duy Hoang Pham
-
A
Semantic Web Based Architecture for e-Contracts in Defeasible
Logic. In A. Adi, S. Stoutenberg and S. Tabet,
editors, Rules and Rule Markup Languages for the Semantic
Web. RuleML 2005, pages 145-159. LNCS 3791, Springer, Berlin,
2005. The original pubblication is available
at www.springerlink.com.
Abstract:
We introduce the DR-CONTRACT architecture to represent and reason on
e-Contracts. The architecture extends the DR-device architecture by
a deontic defeasible logic of violation. We motivate the choice for
the logic and we show how to extend RuleML to capture the notions
relevant to describe e-contracts for a monitoring perspective in
Defeasible Logic.
 
- Guido Governatori and Duy Hoang Pham.
-
DR-CONTRACT: An Architecture for e-Contracts in Defeasible
Logic.
International Journal of Business Process Integration and
Management, 5(4), 2009.
Abstract: We introduce the DR-CONTRACT architecture to represent
and reason on e-Contracts. The architecture extends the DR-device
architecture by a deontic defeasible logic of violation. We motivate the
choice for the logic and we show how to extend RuleML to capture the notions
relevant to describe e-contracts for a monitoring perspective in Defeasible
Logic.
 
- Guido Governatori, Duy Hoang Pham, Simon Raboczi, Andrew
Newman, and Subhasis Thakur.
-
On extending
RuleML for modal defeasible logic.
In Nick Bassiliades, Guido Governatori, and Adrian Paschke, editors,
RuleML 2008: The International RuleML Symposium on Rule Interchange and
Applications, Lecture Notes in Computer Science, Berlin, 2008.
Springer, Copyright © 2008 Springer.
Abstract: In this paper we present a general methodology to
extend Defeasible Logic with modal operators. We motivate the reasons for
this type of extension and we argue that the extension will allow for a
robust knowledge framework in different application areas. The paper presents
an extension of RuleML to capture Modal Defeasible Logic.
 
- Guido Governatori and Antonino Rotolo.
-
A computational framework for non-monotonic
agency, institutionalised power and multi-agent systems.
In Daniéle Bourcier, editor, Legal Knowledge and Inforamtion
Systems, volume 106 of Frontieres in Artificial Intelligence and
Applications, pages 151-152, IOS Press, Amsterdam, 2003.
 
- Guido Governatori and Antonino Rotolo.
-
A defeasible logic of institutional
agency.
In Gerhard Brewka and Pavlos Peppas, editors, NRAC'03, pages 97-104,
Acapulco, Mexico, 10-11 August 2003. IJCAI.
Abstract:A non-monotonic logic of institutional agency is defined
combining a computationally oriented non-monotonic system (Defeasible Logic)
and intensional notions of agency.
 
- Guido Governatori and Antonino Rotolo.
-
Modelling contracts using
RuleML.
In Thomas Gordon, editor, Legal Knowledge and Information Systems,
volume 120 of Frontieres in Artificial Intelligence and
Applications, pages 141-150, Amsterdam, 2004. IOS Press.
Abstract:This paper presents an approach for the specification
and implementation of e-contracts for Web monitoring. This is done in the
setting of RuleML. We argue that monitoring contract execution
requires also a logical account of deontic concepts and of violations.
Accordingly, RuleML is extended to cover these aspects.
 
- Guido Governatori and Antonino Rotolo.
-
Defeasible logic: Agency and obligation.
In Alessio Lomuscio and Donald Nute, editors, Deontic Logic in Computer
Science, number 3065 in LNAI, pages 114-128,
Springer-Verlag, Berlin, 2004. Copyright © 2004 Spinger.
Abstract:We propose a computationally oriented non-monotonic
multi-modal logic arising from the combination of agency, intention and
obligation. We argue about the defeasible nature of these notions and then we
show how to represent and reason with them in the setting of defeasible
logic.
 
- Guido Governatori and Antonino Rotolo.
-
BIO
logical agents: Norms, beliefs, intentions in defeasible logic.
Journal of Autonomous Agents and Multi Agent Systems, 2008.
Copyright © 2008 Springer.
Abstract: In this paper we follow the BOID (Belief, Obligation,
Intention, Desire) architecture to describe agents and agent types in
Defeasible Logic. We argue, in particular, that the introduction of
obligations can provide a new reading of the concepts of intention and
intentionality. Then we examine the notion of social agent (i.e., an agent
where obligations prevail over intentions) and discuss some computational and
philosophical issues related to it. We show that the notion of social agent
either requires more complex computations or has some philosophical
drawbacks.
- Guido Governatori and Antonino Rotolo.
-
Changing
legal systems: Abrogation and annulment. Part I: Revision of defeasible
theories.
In Ron van der Meyden and Leon van der Torre, editors, 9th International
Conference on Deontic Logic in Computer Science (DEON2008), Lecture
Notes in Computer Science. Springer, 2008.
Copyright © 2008 Springer.
Abstract: In this paper we investigate how to model legal
abrogation and annulment in Defeasible Logic. We examine some options that
embed in this setting, and similar rule-based systems, ideas from belief and
base revision. In both cases, our conclusion is negative, which suggests to
adopt a different logical model.
- Guido Governatori and Antonino Rotolo.
-
Changing
legal systems: Abrogation and annulment. Part II: Temporalised defeasible
logic.
In Guido Boella, Harko Verhagen, and Muindhar Singh, editors, Proceedings
of Normative Multi Agent Systems (NorMAS 2008, Luxembourg 15-16 July 2008.
Abstract: In this paper we propose a temporal extension of
Defeasible Logic to model legal modifications, such as abrogation and
annulment. Hence, this framework overcomes the difficulty, discussed
elsewhere \cite{deon-part1}, of capturing these modification types using
belief and base revision.
 
- Guido Governatori and Antonino Rotolo.
-
An
algorithm for business process compliance.
In Enrico Francesconi, Giovani Sartor, and Daniela Tiscornia, editors,
Legal Knowledge and Information Systems (Jurix 2008),
Frontieres in Artificial Intelligence and Applications 189, pages
186-191. IOS Press, 2008.
Abstract: This paper provides a novel mechanism to check whether
business processes are compliant with business rules regulating them. The key
point is that compliance is a relationship between two sets of
specifications: the specifications for executing a business process and the
specifications regulating it.
 
- Guido Governatori and Antonino Rotolo.
-
A
computational framework for institutional agency.
Artificial Intelligence and Law, 16 no. 1 pp. 25-52, 2008,
Copyright © 2008 Springer.
Abstract: This paper provides a computational framework, based on
Defeasible Logic, to capture some aspects of institutional agency. Our
background is Kanger-Lindahl-Pörn account of organised interaction, which
describes this interaction within a multi-modal logical setting. This work
focuses in particular on the notions of counts-as link and on those of
attempt and of personal and direct action to realise states of affairs. We
show how standard Defeasible Logic can be extended to represent these
concepts: the resulting system preserves some basic properties commonly
attributed to them. In addition, the framework enjoys nice computational
properties, as it turns out that the extension of any theory can be computed
in time linear to the size of the theory itself.
- Guido Governatori and Antonino Rotolo.
-
Changing legal systems: legal abrogations and annulments in defeasible
logic.
Logic Journal of IGPL, 18 no. 1 pp. 157-194, 2009.
Copyright © 2010 Oxford University Press.
Abstract: In this paper we investigate how to represent and
reason about legal abrogations and annulments in Defeasible Logic. We examine
some options that embed in this setting, and in similar rule-based systems,
ideas from belief and base revision. In both cases, our conclusion is
negative, which suggests to adopt a different logical model. This model
expresses temporal aspects of legal rules, and distinguishes between two main
timelines, one internal to a given temporal version of the legal system, and
another relative to how the legal system evolves over time. Accordingly, we
propose a temporal extension of Defeasible Logic suitable to express this
model and to capture abrogation and annulment. We show that the proposed
framework overcomes the difficulties discussed in regard to belief and base
revision, and is sufficiently flexible to represent many of the subtleties
characterizing legal abrogations and annulments.
 
- Guido Governatori and Antonino Rotolo.
-
A
conceptually rich model of business process compliance.
In Sebastian Link and Aditya Ghose, editors, 7th Asia-Pacific Conference
on Conceptual Modelling (APCCM 2010), CRPIT. ACS, 2010.
Abstract: In this paper we extend the preliminary work developed
elsewhere and investigate how to characterise many aspects of the compliance
problem in business process modeling. We first define a formal and
conceptually rich language able to represent, and reason about, chains of
reparational obligations of various types. Second, we devise a mechanism for
normalising a system of legal norms. Third, we specify a suitable language
for business process modeling able to automate and optimise business
procedures and to embed normative constraints. Fourth, we develop an
algorithm for compliance checking and discuss some computational issues
regarding the possibility of checking compliance runtime or of enforcing it
at design time.
 
- Guido Governatori and Antonino Rotolo.
-
On the complexity of temporal defeasible logic.
In Thomas Meyer and Eugenia Ternovska, editors, 13 International Workshop
on Non-Monotonic Reasoning (NMR 2010), CEUR Workshop Proceedings, 2010.
Abstract: In this paper we investigate the complexity of temporal
defeasible logic, and we propose an efficient algorithm to compute the
extension of a temporalised defeasible theory. We motivate the logic showing
how it can be used to model deadlines.
 
- Guido Governatori and Antonino Rotolo.
-
Norm
compliance in business process modeling.
In Mike Dean, John Hall, Antonino Rotolo, and Said Tabet, editors, RuleML
2010: 4th International Web Rule Symposium, number 6403 in LNCS, pages
194-209, Berlin, 2010. Springer. Copyrigth © 2010 Springer.
Abstract: We investigate the concept of norm compliance in
business process modeling. In particular we propose an extension of Formal
Contract Logic (FCL), a combination of defeasible logic and a logic of
violation, with a richer deontic language capable of capture many different
facets of normative requirements. The resulting logic, called Process
Compliance Logic (PCL), is able to capture both semantic compliance and
structural compliance. This paper focuses on structural compliance, that is
we show how PCL can capture obligations concerning the structure of a
business process.
 
- Guido Governatori and Rotolo Antonino.
-
Justice delayed is
justice denied: Logics for a temporal account of reparations and legal
compliance.
In João Leite, Paolo Torroni, Thomas Ågotnes, Guido Boella, and Leon van der Torre, editors, CLIMA XII, 12th International Workshop on
Computational Logic and Multi-Agent Sytems, number LNCS. Springer, 2011,
Copyrigth © 2011 Springer.
Abstract: In this paper we extend the logic of violation proposed
by Governatori and Rotolo with time, more precisely, we temporalise that
logic. The resulting system allows us to capture many subtleties of the
concept of legal compliance. In particular, the formal characterisation of
compliance can handle different types of legal obligation and different
temporal constraints over them. The logic is also able to represent, and
reason about, chains of reparative obligations, since in many cases the
fulfillment of these types of obligation still amount to legally acceptable
situations.
 
- Guido Governatori, Antonino Rotolo and
Vineet Padmanabhan.
-
The
Cost of Social Agents. In 5th International Conference
on Autonomous Agents and Multi-Agent Systems (AAMAS06),
pages 513-520. ACM Press, 2006. Copyright ©
2006 ACM.
Abstract: In this paper we follow the BOID (Belief,
Obligation, Intention, Desire) architecture to describe agents and
agent types in Defeasible Logic. We argue that the introduction of
obligations can provide a new reading of the concepts of intention
and intentionality. Then we examine the notion of social agent
(i.e., an agent where obligations prevail over intentions) and
discuss some computational and philosophical issues related to it.
We show that the notion of social agent either requires more complex
computations or has some philosophical drawbacks.
 
-
Guido Governatori, Antonino Rotolo, Régis Riveret, Monica Palmirani and Giovanni Sartor.
-
Variations of Temporal Defeasible Logic for Modelling Norm Modifications.
In Radboud Winkels, editor,
Proceedings of 11th International Conference on Artificial Intelligence and Law, pp 155-159. ACM Press, New York, 2007.
Copyright © 2007 ACM
Abstract: This paper proposes some variants of Temporal Defeasible Logic (TDL) to reason about normative modifications. These variants make it possible to differentiate cases in which, for example, modifications at some time change legal rules but their conclusions persist afterwards from cases where also their conclusions are blocked.
- Guido Governatori, Antonino Rotolo, and Shazia
Sadiq.
-
A
model of dynamic resource allocation in workflow systems.
In Klaus-Dieter Schewe and Hugh E. Williams, editors, Database Technology
2004, number 27 in Conference Research and Practice of Information
Technology, pages 197-206. Australian Computer Science Association, ACS,
2004. Copyright ©
2004 ACS.
Abstract:Current collaborative work environments are
characterized by dynamically changing organizational structures. Although
there have been several efforts to refine work distribution, especially in
workflow management, most literature assumes a static database approach which
captures organizational roles, groups and hierarchies and implements a
dynamic roles based agent assignment protocol. However, in practice only
partial information may be available for organizational models, and in turn a
large number of exceptions may emerge at the time of work assignment. In this
paper we present an organizational model based on a policy based normative
system. The model is based on a combination of an intensional logic of agency
and a flexible, but computationally feasible, non-monotonic formalism
(Defeasible Logic). Although this paper focuses on the model specification,
the proposed approach to modelling agent societies provides a means of
reasoning with partial and unpredictable information as is typical of
organizational agents in workflow systems.
 
- Guido Governatori, Antonino Rotolo, and Rossella
Rubino.
-
Implementing temporal defeasible logic for modeling legal reasoning.
In 3rd Juris-Informatics Workshop (Jurisin 2009), LNAI, Berlin,
2010. Springer, Copyright © 2010 Springer.
Abstract: In this paper we briefly present an efficient
implementation of temporal defeasible logic, and we argue that it can be used
to efficiently capture the the legal concepts of persistence, retroactivity
and periodicity. In particular, we illustrate how the system works with a
real life example of a regulation.
 
- Guido Governatori, Antonino
Rotolo, and Giovanni Sartor.
-
Temporalised normative positions in defeasible logic. In Anne Gardner,
editor, Procedings of the 10th International Conference on
Artificial Intelligence and Law, pages 25-34. ACM Press, 2005,
Copyright
© 2005 ACM.
Abstract:We propose a computationally oriented
non-monotonic multi-modal logic arising from the combination of
temporalised agency and temporalised normative positions. We argue
about the defeasible nature of these notions and then we show how to
represent and reason with them in the setting of Defeasible Logic.
 
- Guido Governatori and Shazia Sadiq.
-
The journey to business process
compliance.
In Jorge Cardoso and Wil van der Aalst, editors, Handbook of Research on
BPM, IGI Global, 2009.
Abstract: It is a typical scenario that many organisations have
their business processes specified independently of their business
obligations (which includes contractual obligations to business partners, as
well as obligations a business has to fulfil against regulations and industry
standards). This is because of the lack of guidelines and tools that
facilitate derivation of processes from contracts but also because of the
traditional mindset of treating contracts separately from business processes.
This chapter will provide a solution to one specific problem that arises from
this situation, namely the lack of mechanisms to check whether business
processes are compliant with business contracts. The chapter begins by
defining the space for business process compliance and the eco-system for
ensuring that process are compliant. The key point is that compliance is a
relationship between two sets of specifications: the specifications for
executing a business process and the specifications regulating a business.
The central part of the chapter focuses on a logic based formalism for
describing both the semantics of normative specifications and the semantics
of compliance checking procedures.
 
- Guido Governatori and Giovanni Sartor.
-
Burdens
of proof in monological argumentation.
In Radboud Winkels, editor, Legal Knowledge and Information Systems JURIX
2010: The Twenty-Third Annual Conference, Frontiers in Artificial
Intelligence and Applications, Amsterdam, 2010. IOS Press.
Abstract: We shall argue that burdens of proof are relevant also
to monological reasoning, i.e., for deriving the conclusions of a
knowledge-base allowing for conflicting arguments. Reasoning with burdens of
proof can provide a useful extension of current argument-based non-monotonic
logics, at least a different perspective on them. Firstly we shall provide an
objective characterisation of burdens of proof, assuming that burdens
concerns rule antecedents (literals in the body of rules), rather than
agents. Secondly, we shall analyse the conditions for a burden to be
satisfied, by considering credulous or skeptical derivability of the
concerned antecedent or of its complement. Finally, we shall develop a method
for developing inferences out of a knowledge base merging rules and proof
burdens in the framework of defeasible logic.
 
- Guido Governatori and Paolo Terenziani.
-
Temporal extensions to defeasible logic.
In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint
Conference on Artificial Intelligence, AI 2007, Gold Coast, 2-6 December
2007. Copyright © 2007 Springer. The original publication is available at
www.springerlink.com.
Abstract: In this paper, we extend Defeasible Logic (a
computationally-oriented non-monotonic logic) in order to deal with
temporalised rules. In particular, we extend the logic to cope with durative
facts, as well as with delays between the antecedent and the consequent of
rules. We showed that the extended temporalised framework is suitable to
model different types of causal relations which have been identified by the
specialised literature. We also prove that the computational properties of
the original logic are still retained by the extended approach.
 
- Guido Governatori, Subhasis Thakur, and Duy Hoang
Pham.
-
A
compliance model of trust.
In Enrico Francesconi, Giovani Sartor, and Daniela Tiscornia, editors,
Legal Knowledge and Information Systems (Jurix 2008),
Frontieres in Artificial Intelligence and Applications 189, pages
118-127. IOS Press, 2008.
Abstract: We present a model of past interaction trust model
based on compliance of expected behaviours.
 
- Guido Governatori and Andrew Stranieri.
-
Towards the application of association rules
for defeasible rules discovery.
In Bart Verheij, Arno Lodder, Ronald P. Loui, and Antoniette J. Muntjerwerff,
editors, Legal Knowledge and Information Systems, pages 63-75,
Amsterdam, 2001. JURIX, IOS Press.
Abstract:In this paper we investigate the feasibility of
Knowledge Discovery from Database (KDD) in order to facilitate the discovery
of defeasible rules that represent the ratio decidendi underpinning legal
decision making. Moreover we will argue in favour of Defeasible Logic as the
appropriate formal system in which the extracted principles should be
encoded.
 
- Guido Governatori and Paolo Terenziani.
- Temporal extensions to defeasible logic.
In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint
Conference on Artificial Intelligence, AI 2007,
LNAI 4830, pages 476-485. Springer, 2007.
Copyright © 2007 Springer.
Abstract: In this paper, we extend Defeasible Logic (a
computationally-oriented non-monotonic logic) in order to deal with
temporalised rules. In particular, we extend the logic to cope with durative
facts, as well as with delays between the antecedent and the consequent of
rules. We showed that the extended temporalised framework is suitable to
model different types of causal relations which have been identified by the
specialised literature. We also prove that the computational properties of
the original logic are still retained by the extended approach.
- Guido Governatori, Arthur H.M. ter Hofstede, and
Phillipa Oaks.
-
Defeasible logic for automated
negotiation.
In P. Swatman and P.M. Swatman, editors, Proceedings of CollECTeR.
Deakin University, 2000.
Published on CD.
Abstract:Negotiation plays a fundamental role in e-commerce. In
this paper, the application of defeasible logic for automated negotiation is
investigated. Defeasible logic is flexible enough to be adapted to several
possible negotiation strategies, has efficient implementations, and provides
a formal basis for analysis (e.g. to explain why a negotiation was not
successful). Two case studies, one small and one more comprehensive, will be
described and the feasibility of approaches based on defeasible logic will be
discussed.
 
- Guido Governatori, Arthur H.M. ter Hofstede, and
Phillipa Oaks.
-
Is defeasible logic applicable?.
In Grigoris Antoniou and Guido Governatori, editors, Proceedings of the
2nd Australasian Workshop on Computational Logic, pages 47-62, Brisbane,
January 2001. Queensland University of Technology.
Abstract:In this paper the application of defeasible logic for
automated negotiation is investigated. Defeasible logic is flexible enough to
be adapted to several possible negotiation strategies, has efficient
implementations, and provides a formal basis for analysis (e.g. to explain
why a negotiation was not successful). Two case studies, one small and one
more comprehensive, will be described and the feasibility of approaches based
on defeasible logic will be discussed.
 
- Benjamin Johnston and Guido Governatori.
- Induction
of defeasible logic theories in the legal domain. In Giovanni
Sartor, editor, Procedings of the 9th International Conference
on Artificial Intelligence and Law, pages 204-213. IAAIL, ACM
Press,
2003. Copyright
© 2003 ACM.
Abstract:The market for intelligent legal information systems
remains relatively untapped and while this might be interpreted as an
indication that it is simply impossible to produce a system that satisfies
the needs of the legal community, an analysis of previous attempts at
producing such systems reveals a common set of deficiencies that in-part
explain why there have been no overwhelming successes to date. Defeasible
logic, a logic with proven successes at representing legal knowledge, seems
to overcome many of these deficiencies and is a promising approach to
representing legal knowledge. Unfortunately, an immediate application of
technology to the challenges in this domain is an expensive and
computationally intractable problem. So, in light of the benefits, we seek to
find a practical algorithm that uses heuristics to discover an approximate
solution. As an outcome of this work, we have developed an algorithm that
integrates defeasible logic into a decision support system by automatically
deriving its knowledge from databases of precedents. Experiments with the new
algorithm are very promising - delivering results comparable to and
exceeding other approaches.
 
- Benjamin Johnston and Guido Goverantori.
-
An algorithm for the induction of defeasible
logic theories from databases.
In Klaus-Dieter Schewe and Xiaofang Zhou, editors, Database Technology
2003, number 17 in Conference Research and Practice of Information
Technology, pages 75-83. Australian Computer Science Association, ACS, 4-7
February 2003. Copyright ©
2003 ACS.
Abstract:Defeasible logic is a non-monotonic logic with
applications in rule-based domains such as law. To ease the development and
improve the accuracy of expert systems based on defeasible logic, it is
desirable to automatically induce a theory of the logic from a training set
of precedent data. Empirical evidence suggests that minimal theories that
describe the training set tend to be more faithful representations of
reality. We show via transformation from the hitting set problem that this
global minimization problem is intractable, belonging to the class of NP
optimisation problems. Given the inherent difficulty of finding the optimal
solution, we instead use heuristics and demonstrate that a best-first,
greedy, branch and bound algorithm can be used to find good theories in short
time. This approach displays significant improvements in both accuracy and
theory size as compared to recent work in the area that post-processed the
output of an Aprori association rule-mining algorithm, with comparable
execution times.
 
- Efsrations Kontopoulos, Nick Bassiliades, Guido
Governatori, and Grigoris Antoniou.
-
Extending
a defeasible reasoner with modal and deontic logic operators.
In 2008 IEEE/WIC/ACM International Conference on Web Intelligence and
Intelligent Agent Technology, pages 626-629. IEEE Press,
2008, Copyright ©
2008 IEEE.
Abstract: Defeasible logic is a non-monotonic formalism that
deals with incomplete and conflicting information. Modal logic deals with
necessity and possibility, exhibiting defeasibility; thus, it is possible to
combine defeasible logic with modal operators. This paper reports on the
extension of the DR-DEVICE defeasible reasoner with modal and deontic logic
operators. The aim is a practical defeasible reasoner that will take
advantage of the expressiveness of modal logics and the flexibility to define
diverse agent types and behaviors.
 
- Ho-Pun Lam and Guido Governatori.
-
The making of SPINdle.
In Guido Governatori, John Hall, and Adrian Paschke, editors, Rule
Representation, Interchange and Reasoning on the Web, number 5858 in
LNCS, Berlin, 5-7 November 2009. Springer, Copyright © 2009 Springer.
Abstract: We present the design and implementation of SPINdle
&emdash; an open source Java based defeasible logic
reasoner capable to perform efficient and scalable
reasoning on defeasible logic theories (including
theories with over 1 million rules). The
implementation covers both the standard and modal
extensions to It allows users or agents to issues
queries, on a given knowledge base or a theory
generated on the fly by other applications, and
automatically produces the conclusions of its
consequences. The theory can also be represented
using XML.
 
- Ho-Pun Lam and Guido Governatori.
-
On the problem of computing ambiguity propagation and
well-founded semantics in defeasible logic.
In Mike Dean, John Hall, Antonino Rotolo, and Said Tabet, editors, RuleML
2010: 4th International Web Rule Symposium, number 6403 in LNCS, pages
119-127, Berlin, 2010. Springer, ">Copyrigth © 2010 Springer.
Abstract: In this paper we present the well founded variants of
ambiguityblocking and ambiguity propagating defeasible logics. We also show
how to extend SPINdle, a state of the art, defeasible logic implementation to
handle all such variants of defeasible logic.
 
- Ho-Pun Lam and Guido Governatori.
-
Towards a model of
UAVs navigation in urban canyon through defeasible logic.
Journal of Logic and Computation, 2011.
Abstract: This paper shows how a non-monotonic rule based system
(defeasible logic) can be integrated with numerical computation engines, and
how this can be applied to solve the Vehicle Routing Problem (VRP). To this
end, we have simulated a physical system from which we can obtain numerical
information. The physical system perceives information from its environment
and generates predicates that can be reasoned by a defeasible logic engine.
The conclusions/decisions derived will then realized by the physical system
as it takes actions based on the conclusion derived. Here we consider a
scenario where a ``flock'' of UAVs have to navigate within an urban canyon
environment. The UAVs are self-autonomous without centralized control. The
goal of the UAVs is to navigate to their desired destinations without
colliding with each other. In case of possible collision, the UAVs concerned
will communicate with each other and use their background knowledge or travel
guidelines to resolve the conflicts.
 
- Ho-Pun Lam and Guido Governatori.
-
What are the
necessity rules in defeasible reasoning?.
In James Delgrande and Wolfgang Faber, editors, 11th International
Conference on Logic Programming and Nonmonotonic Reasoning (LPNMAR
2011), Lecture Notes in Computer Science. Springer, 2011.
Copyrigth © 2011 Springer.
Abstract: This paper investigates a new approach for computing
the inference of defeasible logic. The algorithm proposed can substantially
reduced the theory size increase due to transformations while preserving the
representation properties in different variants of DL. Experiments also show
that our algorithm outperform traditional approach by several order of
amplitudes.
 
- Michael J. Maher and Guido Governatori.
-
A semantic decomposition of defeasible
logic.
In Proc. American National Conference on Artificial Intelligence
(AAAI-99), pages 299-305, Menlo Park, CA, 1999. AAAI Press,
Copyright © 1999 AAAI, American Association for Artificial Intelligence.
Abstract:We investigate defeasible logics using a technique which
decomposes the semantics of such logics into two parts: a specification of
the structure of defeasible reasoning and a semantics for the meta-language
in which the specification is written. We show that Nute's Defeasible Logic
corresponds to Kunen's semantics, and develop a defeasible logic from the
well-founded semantics of Van Gelder, Ross and Schlipf. We also obtain a new
defeasible logic which extends an existing language by modifying the
specification of Defeasible Logic. Thus our approach is productive in
analysing, comparing and designing defeasible logics.
 
- Duy Hoang Pham, Guido Governatori, and Simon Raboczi.
-
Agents
adapt to majority behaviours.
In The 2008 IEEE International Conference on Research, Innovation and
Vision for the Future, 2008. RIVF'08, IEEE, 2008, Copyright © 2008
IEEE.
Abstract: Agents within a group can have different perceptions of
their working environment and autonomously fulfil their goals. However, they
can be aware of beliefs and goals of the group as well as other members so
that they can adjust their behaviours accordingly. To model these agents, we
explicitly include knowledge commonly shared by the group and that obtained
from other agents. By avoiding actions which violate ``mental attitudes''
shared by the majority of the group, agents demonstrate their social
commitment to the group. Defeasible logic is chosen as our representation
formalism for its computational efficiency, and for its ability to handle
incomplete and conflicting information. Hence, our agents can enjoy the low
computational cost while performing ``reasoning about others''. Finally, we
present the implementation of our multi-agent system.
 
- Duy Hoang Pham, Subhasis Thakur, and Guido Governatori.
-
Defeasible logic to
model n-person argumentation game.
In Maurice Pagnuco and Michael Thielscher, editors, Twelfth International
Workshop on Non-Monotonic Reasoning, pages 215-222, 13--15 September
2008.
Abstract: In multi-agent systems, an individual agent can pursue
its own goals, which may conflict with those hold by other agents. To settle
on a common goal for the group of agents, the argumentation/dialogue game
provides a robust and flexible tool where an agent can send its explanation
for its goal in order to convince other agents. In the setting that the
number of agents is greater than two and they are equally trustful, it is not
clear how to extend existing argumentation/dialogue frameworks to tackle
conflicts from many agents. We propose to use the defeasible logic to model
the n-person argumentation game and to use the majority rule as an additional
preference mechanism to tackle conflicts between arguments from individual
agents.
 
- Duy Hoang Pham, Guido Governatori, and Subhasis Thakur.
-
Extended defeasible reasoning for common goals in n-person argumentation
games.
Journal of Universal Computer Science, 15 no. 13 pp.
2653--2675, 2009.
Abstract: Argumentation games have been proved to be a robust and
flexible tool to resolve conflicts among agents. An agent can propose its
explanation and its goal known as a claim, which can be refuted by other
agents. The situation is more complicated when there are more than two agents
playing the game. We propose a weighting mechanism for competing premises to
tackle with conflicts from multiple agents in an n-person game. An agent can
defend its proposal by giving a counter-argument to change the "opinion" of
the majority of opposing agents. Furthermore, using the extended defeasible
reasoning an agent can exploit the knowledge that other agents expose in
order to promote and defend its main claim.
 
- Pakornpong Pothipruk and Guido Governatori.
-
ALE Defeasible Description Logic.
In Abdul Sattar and Byeong Ho Kang, editor,
19th Australian Joint Conference on Artificial Intelligence,
Hobart. pages 110-119. Lecture Notes in Computer Science 4304.
Springer, Berlin, 2006. The original publication is available at
www.springerlink.com
Abstract: One of Semantic Web strengths is the ability to
address incomplete knowledge. However, at present, it cannot handle
incomplete knowledge directly. Also, it cannot handle non-monotonic
reasoning. In this paper, we extend ALC-. Defeasible Description
Logic with existential quantifier, i.e., ALE Defeasible
Description Logic. Also, we modify some parts of the logic,
resulting in an increasing efficiency in its reasoning.
- Régis Riveret, Guido Governatori,
and Antonino Rotolo.
-
Argumentation semantics for temporal defeasible logic.
In Pavlos Peppas, Anna Perini, and Loris Penserini, editors, Third
European Starting AI Researcher Symposium (STAIRS 2006), pages
267-268, Riva del Garda, 28-29 August 2006. IOS Press, Amsterdam, 2006.
Abstract:
We present an extension of the argumentation semantics
for defeasible logic to cover the temporalisation of defeasible logic with
permanent and immanent temporal literals.
 
- Régis Riveret, Antonino Rotolo and
Guido Governatori.
-
Interaction between Normative Systems and Cognitive agents in
Temporal Modal Defeasible Logic. In Guido Boella, Leon van der
Torre and Harko Verhagen, editors, Normative Multi-agent
Systems. Dagstuhl Seminar Proceedings 7122. Internationales
Begegnungs- und Forschungszentrum fuer Informatik (IBFI), Schloss
Dagstuhl, Germany, Dagstuhl, Germany, 2007.
Abstract: While some recent frameworks on cognitive agents
addressed the combination of mental attitudes with deontic concepts,
they commonly ignore the representation of time. We propose in this
paper a variant of Temporal Modal Defeasible Logic to deal in
particular with temporal intervals.
 
- Bram Roth, Régis Riveret, Antonino Rotolo and
Guido Governatori.
-
Strategic Argumentation: A Game Theoretical Investigation.
In Radboud Winkels, editor,
Proceedings of 11th International Conference on Artificial Intelligence and Law, pp 81-90. ACM Press, New York, 2007.
Copyright © 2007 ACM
Abstract: Argumentation is modelled as a game where the payoffs are measured in terms of the probability that the claimed conclusion is, or is not, defeasibly provable, given a history of arguments that have actually been exchanged, and given the probability of the factual premises. The probability of a conclusion is calculated using a standard variant of Defeasible Logic, in combination with standard probability calculus. It is a new element of the present approach that the exchange of arguments is analysed with game theoretical tools, yielding a prescriptive and to some extent even predictive account of the actual course of play. A brief comparison with existing argument-based dialogue approaches confirms that such a prescriptive account of the actual argumentation has been almost lacking in the approaches proposed so far.
- Thomas Skylogiannis, Grigoris Antoniou,
Nick Bassiliades, and Guido Governatori.
-
DR-NEGOTIATE - a system for
automated agent negotiation with defeasible logic-based strategies.
In Proceedings of The 2005 IEEE International Conference on e-Technology,
e-Commerce and e-Service, 2005. EEE'05, pages 44-49. IEEE Press, 29
March - 1 April 2005, Copyright © 2005 IEEE.
Abstract:This paper reports on a system for automated agent
negotiation. It uses the JADE agent framework, and its major distinctive
feature is the use of declarative negotiation strategies. The negotiation
strategies are expressed in a declarative rules language, defeasible logic
and are applied using the implemented defeasible reasoning system DR-DEVICE.
The choice of defeasible logic is justified. The overall system architecture
is described, and a particular negotiation case is presented in detail.
 
- Thomas Skylogiannis, Grigoris Antoniou,
Nick Bassiliades, Guido Governatori and Antonis Bikakis.
-
DR-NEGOTIATE — A System for Automated Agent Negotiation with Defeasible Logic-Based Strategies.
Data & Knowledge Engineering: 2007.
Copyright © 2007 Elsevier B.V.
Abstract: This paper reports on a system for automated agent negotiation, based on a formal and executable approach to capture the behavior of parties involved in a negotiation. It uses the JADE agent framework, and its major distinctive feature is the use of declarative negotiation strategies. The negotiation strategies are expressed in a declarative rules language, defeasible logic, and are applied using the implemented system DR-DEVICE. The key ideas and the overall system architecture are described, and a particular negotiation case is presented in detail.
- Insu Song and Guido Governatori
- Nested
Rules in Defeasible Logic. In A. Adi, S. Stoutenberg and
S. Tabet, editors, Rules and Rule Markup Languages for the
Semantic Web. RuleML 2005, pages 204-208. LNCS 3791, Springer,
Berlin, 2005. The original pubblication is available
at www.springerlink.com.
Abstract:
Defeasible Logic is a rule-based non-monotonic logic with
tractable reasoning services. In this paper we extend Defeasible
Logic with nested rules. We consider a new Defeasible Logic,
called DL$^{ns}$, where we allow one level of nested rules. A
nested rule is a rule where the antecedent or the consequent of
the rule are rules themselves. The inference conditions for
DL$^{ns}$ are based on reflection on the inference structures
(rules) of the particular theory at hand. Accordingly DL$^{ns}$
can be considered an amalgamated reflective system with implicit
reflection mechanism. Finally we outline some possible
applications of the logic.
 
- Subhasis Thakur, Guido Governatori, Vineet
Padmanabhan, and Jenny Eriksson Lundström.
-
Dialogue games in defeasible logic.
In Mehmet A. Orgun and John Thornton, editors, 20th Australian Joint
Conference on Artificial Intelligence, AI 2007,
LNAI 4830, pages 497-506. Springer, 2007.
Copyright © 2007 Springer.
Abstract: In this paper we show how to capture dialogue games in
Defeasible Logic. We argue that Defeasible Logic is a natural candidate and
general representation formalism to capture dialogue games even with
requirements more complex than existing formalisms for this kind of games. We
parse the dialogue into defeasible rules with time of the dialogue as time of
the rule. As the dialogue evolves we allow an agent to upgrade the strength
of unchallenged rules. The proof procedures of (Antoniou, Billington, Governatori, Maher 2001) are used to
determine the winner of a dialogue game.