Papers by Leendert Van Der Torre
Input/Output Consequence Relations: Reasoning with Intensional Contexts
The input/output (I/O) logics introduced by D. Makinson and L. van der Torre in 2000 (and subsequ... more The input/output (I/O) logics introduced by D. Makinson and L. van der Torre in 2000 (and subsequently treated in several other papers) fo- cus on a new kind of abstract reasoning structure devoted to the study of conditional goals and obligations. The original I/O logics dealt ex- clusively with the classical propositional consequence relation by adding certain \black boxes" which
In this paper we use recursive modelling to formalize sanction-based obligations in a qualitative... more In this paper we use recursive modelling to formalize sanction-based obligations in a qualitative game theory. In particular, we formalize an agent who attributes mental attitudes such as goals and desires to the normative sys- tem which creates and enforces its obligations. The wishes (goals, desires) of the normative system are the commands (obligations) of the agent. Since the agent
In a previous paper we developed a general theory of input/output logics. These are operations re... more In a previous paper we developed a general theory of input/output logics. These are operations resembling inference, but where inputs need not be included among outputs, and outputs need not be reusable as inputs. In the present paper we study what happens when they are constrained to render output consistent with input. This is of interest for deontic logic, where it provides a manner of handling contrary-to-duty obligations. Our procedure is to constrain the set of generators of the input/output system, considering only the maximal subsets that do not yield output conflicting with a given input. When inputs are authorised to reappear as outputs, both maxichoice revision in the sense of Alchourrón/Makinson and the default logic of Poole emerge as special cases, and there is a close relation with Reiter default logic. However, our focus is on the general case where inputs need not be outputs. We show in what contexts the consistency of input with output may be reduced to its consistency with a truth-functional combination of components of generators, and under what conditions constrained output may be obtained by a derivation that is constrained at every step.
Annals of Mathematics and Artificial Intelligence, 1999
In this paper we introduce Prohairetic Deontic Logic (PDL), a preference-based dyadic deontic log... more In this paper we introduce Prohairetic Deontic Logic (PDL), a preference-based dyadic deontic logic. In our preference-based interpretation of obligations "α should be (done) if β is (done)" is true if (1) no ¬α∧β state is as preferable as an α∧β state and (2) the preferred β states are α states. We show that this representation solves different problems of deontic logic. The first part of the definition is used to formalize contrary-to-duty reasoning, which, for example, occurs in Chisholm's and Forrester's notorious deontic paradoxes. The second part is used to make deontic dilemmas inconsistent.
Lecture Notes in Computer Science, 2005
In this paper we propose a new role for the agent metaphor in the definition of the organizationa... more In this paper we propose a new role for the agent metaphor in the definition of the organizational structure of multiagent systems. The agent metaphor is extended to consider as agents also social entities like organizations, groups and normative systems, so that mental attitudes can be attributed to them -beliefs, desires and goals -and also an autonomous and proactive behavior. We show how the metaphor can be applied also to structure organizations in functional areas and roles, which are described as agents too. Thus, the agent metaphor can play a role similar to the object oriented metaphor which allows structuring objects in component objects. Finally, we discuss how the agent metaphor addresses the problems of control and communication in such structured organizations.
Proceedings of the 9th international conference on Artificial intelligence and law - ICAIL '03, 2003
Proceedings of the 6th international conference on Electronic commerce - ICEC '04, 2004
In this paper we address the problem of defining roles in organizations like e-trade ones. The me... more In this paper we address the problem of defining roles in organizations like e-trade ones. The methodology we use is to model roles according to the agent metaphor: we attribute to roles mental attitudes, like beliefs, desires and goals, we relate them to the agent's required expertise and responsibilities, and we model role behavior in game theoretic terms. Analogously, the organization is modelled as an agent which acts as a normative system: it imposes obligations to roles and to the agents playing the roles.
NORM NEGOTIATION IN MULTIAGENT SYSTEMS
International Journal of Cooperative Information Systems, 2007
Normative multiagent systems provide agents with abilities to autonomously devise societies and o... more Normative multiagent systems provide agents with abilities to autonomously devise societies and or- ganizations coordinating their behavior via social norms and laws. In this paper we study how agents negotiate new social norms and when they accept them. We introduce a negotiation model based on what we call the social delegation cycle, which explains the negotiation of new social norms from agent desires in three steps. First individual agents or their representatives negotiate social goals, then a social goal is negotiated in a social norm, and finally the social norm is accepted by the agents when it leads to fulfilment of the desires the cycle started with. We characterize the allowed propos- als during social goal negotiation as mergers of the individual agent desires, and we characterize the allowed proposals during norm negotiation as both joint plans to achieve the social goal (obligations associated with the norm) and the associated sanctions or rewards (a control system associated with the norm). The norm is accepted when the norm is stable in the sense that agents will act according to the norm, and effective in the sense that fulfilment of the norm leads to achievement of the agents' de- sires. We also compare norm negotiation with contract negotiation and negotiation of the distribution of obligations.
Dagstuhl Seminars, 2007
Judgment aggregation studies how agent opinions on logically in- terconnected propositions can be... more Judgment aggregation studies how agent opinions on logically in- terconnected propositions can be mapped into a collective judg- ment on the same propositions, and is plagued by impossibility re- sults. In this paper we study the central notion of independence in these impossibility results. First, we argue that the distinction be- tween the premises and conclusions play an important role
Lecture Notes in Computer Science, 2005
We study the design of policies for virtual communities of agents based on peer-to-peer systems o... more We study the design of policies for virtual communities of agents based on peer-to-peer systems or the grid infrastructure. In a virtual community agents can play both the role of resource consumers and the role of resource providers. Moreover, the agents remain in control of their resources, and therefore we distinguish between the authorization to access a resource given by the virtual community and the permission to do so issued by the resource providers. We propose a logical multiagent framework for virtual communities that distinguishes three roles: resource consumption, provision, as well as authorization.
Non-Monotonic Reasoning, 2004
We study conflicts between goals and plans in Dung's abstract argumentation framework. Argume... more We study conflicts between goals and plans in Dung's abstract argumentation framework. Argumentation theory has tradi- tionally been used to deal with conflicts between defaults and beliefs. Recently Amgoud has proposed to use it for conflicts between plans. Amgoud argues that Dung's argumentation theory has to be adjusted, because conflicts between plans are fundamentally different from conflicts between defaults. We
Proceedings of the fifth international joint conference on Autonomous agents and multiagent systems - AAMAS '06, 2006
In this paper we illustrate how a role-based semantics for agent communication languages can embe... more In this paper we illustrate how a role-based semantics for agent communication languages can embed the two main existing models of agent communication languages, respectively based on 'mental attitudes' and 'social commitments' semantics. These two models have been presented as incompatible approaches, but recently we illustrated for persuasion dialogues and using our normative multiagent systems framework, that they can be seen also as complimentary ones. Independently from our own multi-agent model, in this paper we illustrate for the speech act 'inform' how the role based semantics embeds the other two semantics.
Lecture Notes in Computer Science, 2006
There are two main traditions in defining a semantics for agent communication languages, based ei... more There are two main traditions in defining a semantics for agent communication languages, based either on mental attitudes or on social commitments. In this paper, we translate both traditions in a different approach in which the dialogue state is represented by the beliefs and goals publicly attributed to the roles played by the dialogue participants. On the one hand, this approach avoids the problems of mentalistic semantics, such as the unverifiability of private mental states. On the other hand, it allows to reuse the logics and implementations developed for FIPA compliant approaches.
2006 IEEE/WIC/ACM International Conference on Intelligent Agent Technology, 2006
We consider agents having multiple communication sessions at the same time. We assume that FIPA s... more We consider agents having multiple communication sessions at the same time. We assume that FIPA semantics of agent communication languages can still be used when we attribute mental attitudes for each session, which we call the roles of the agents, and we assume that we have to distinguish the mental attitudes attributed to the roles from the mental attitudes of the agents. We consider several consequences of the distinction between the mental attitudes attributed to the roles and the mental attitudes attributed to the agent. First, in attributing mental attitudes to an agent or to one of its roles, we argue that only mental attributes are attributed to an agent's role when these attributes follow directly from the agent's communication. They are therefore public in the sense that every agent who has overheard the session, has the same beliefs about the mental attitudes of the role. Second, the moves permitted to the dialogue participants in the same dialogue game are based on the role only, such that different kind of moves can be specified in different types of dialogue games. Obligations are associated to roles related to institutions which can enforce them by means of sanctions. Third, expectations are based both on the mental attitudes ascribed to the agent and to the role.
An Attacker Model for Normative Multi-agent Systems
Lecture Notes in Computer Science, 2007
In this paper we introduce a formal attacker model for normative multi-agent systems. In this con... more In this paper we introduce a formal attacker model for normative multi-agent systems. In this context, an attacker is an agent trying to profit from norm violation, for example because the violation is not detected, it is not being sanctioned, or the sanction is less than the profit of violation. To deliberate about norm violations, an attacker has a self model and a model of the normative multi-agent system, which in our case have the same structure. Moreover, we assume that an attacker violates a norm only when it profits from it, and the attacker therefore plays a violation game with the system. On a variety of examples, we show also how our model of violation games based also on agent abilities or power extends our earlier model based on motivations only.
Lecture Notes in Computer Science, 2006
Logical architectures combine several logics into a more complex logical system. In this paper we... more Logical architectures combine several logics into a more complex logical system. In this paper we study a logical architecture using input/output operations corresponding to the functionality of logical components. We illustrate how the architectural approach can be used to develop a logic of a normative system based on logics of counts-as conditionals, institutional constraints, obligations and permissions. In this example we adapt for counts-as conditionals and institutional constraints a proposal of Jones and Sergot, and for obligations and permissions we adapt the input/output logic framework of Makinson and van der Torre. We use our architecture to study logical relations among counts-as conditionals, institutional constraints, obligations and permissions. We show that in our logical architecture the combined system of counts-as conditionals and institutional constraints reduces to the logic of institutional constraints, which again reduces to an expression in the underlying base logic. Counts-as conditionals and institutional constraints are defined as a pre-processing step for the regulative norms. Permissions are defined as exceptions to obligations and their interaction is characterized.
Prohairetic Deontic Logic (PDL)
Lecture Notes in Computer Science, 1998
Abstract. In this paper we introduce Prohairetic Deontic Logic (PDL), a preference-based dyadic d... more Abstract. In this paper we introduce Prohairetic Deontic Logic (PDL), a preference-based dyadic deontic logic. An obligation 'α should be (done) if β is (done)' is true if (1) no ¬α∧β state is as preferable as an α∧β state and (2) the preferred β states are α states. We show that the ...
Lecture Notes in Computer Science, 2006
In this paper we propose a foundational ontology of the social concepts of organization and role ... more In this paper we propose a foundational ontology of the social concepts of organization and role which structure institutions. We identify which axioms model social concepts like organization and role and which properties distinguish them from other categories like objects and agents: the organizational structure of institutions, the relation between roles and organizations, and the powers among the components of an organization. All social concepts depend on descriptions defining them, which are collectively accepted, and the description defining the components of organizations, including roles, are included in the description of the organizations they belong to. Thus, the relational dependence of roles means that they are defined in the organizations they belong to. Finally, powers inside organizations are defined by the fact that components of an organization can access the state of the organization whose definition they depend on and of the other components, thus violating the standard encapsulation principle of objects.
Proceedings IEEE/WIC International Conference on Web Intelligence (WI 2003), 2003
In this paper we study the rational balance between local and global policies in web based distri... more In this paper we study the rational balance between local and global policies in web based distributed systems. We use a logical framework for multiagent systems to model obligations and permissions composing policies. In particular, a qualitative decision theory allows agents to trade off the decision of respecting a norm against the consequences of not respecting it: the possibility that they are considered violators and thus sanctioned. Global policies refer not to the existence of a local norm but to the fact that it is enforced by the local authority by recognizing and sanctioning violations.
Proceedings of the 38th Annual Hawaii International Conference on System Sciences, 2005
In this paper we propose a conceptual model of virtual organizations as normative multiagent syst... more In this paper we propose a conceptual model of virtual organizations as normative multiagent systems. The dynamic aspects of virtual organizations are modeled using aspects of speech act theory and Searle's theory of the construction of social reality. We illustrate the use of our model by discussing an example of distributed access control policies. We show how the model captures the distinction between local and global authorities, and between local and global norm enforcement policies.
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Papers by Leendert Van Der Torre