Showing papers by "Wiebe van der Hoek published in 2005"

A logic for strategic reasoning

Abstract: Rational strategic reasoning is the process whereby an agent reasons about the best strategy to adopt in a given multi-agent scenario, taking into account the likely behaviour of other participants in the scenario, and, in particular, how the agent's choice of strategy will affect the choices of others We present CATL, a logic that is intended to facilitate such reasoning CATL is an extension of Alternating-time Temporal Logic (ATL), which supports reasoning about the abilities of agents and their coalitions in game-like multi-agent systems CATL extends ATL with a ternary counterfactual commitment operator of the form Ci(σ, φ), with the intended reading "if it were the case that agent i committed to strategy σ, then φ" By using this operator in combination with the ability operators of ATL, it is possible to reason about the implications of different possible choices by agents We illustrate the approach by showing how CATL may be used to express properties of games such as Nash equilibrium and Pareto efficiency We also show that the model checking problem for CATL is tractable, and hence that efficient implementations of strategic reasoners based on CATL are feasible

Intentions and strategies in game-like scenarios

Abstract: In this paper, we investigate the link between logics of games and “mentalistic” logics of rational agency, in which agents are characterized in terms of attitudes such as belief, desire and intention. In particular, we investigate the possibility of extending the logics of games with the notion of agents’ intentions (in the sense of Cohen and Levesque’s BDI theory). We propose a new operator (straσ) that can be used to formalize reasoning about outcomes of strategies in game-like scenarios. We briefly discuss the relationship between intentions and goals in this new framework, and show how to capture dynamic logic-like constructs. Finally, we demonstrate how game-theoretical concepts like Nash equilibrium can be expressed to reason about rational intentions and their consequences.

Knowledge and social laws

Abstract: In this paper we combine existing work in the area of social laws with a framework for reasoning about knowledge in multi-agent systems. The unifying framework in which this is done is based on Alternating-time Temporal Logic (ATL), to which semantics we add epistemic accessibility relations (to deal with the knowledge), actions (in order to naturally talk about allowed and forbidden actions) and updates (to model the effect of the implementation of the constraint in a social law). Apart from a constraint, a social law has an objective: in our formalism, such objectives may refer to the knowledge that agents possess or do not possess. The result is a framework in which we can, for example, express that a desirable property (objective) of a social law is that one agent has the ability to bring about a certain type of knowledge in another agent, or that if one agent knows something, then it should behave in a certain way. We illustrate our approach with a case study, and we use model checking to demonstrate that properties of social laws with respect to this case study.

On the dynamics of delegation, cooperation, and control: a logical account

Abstract: We present DCL-PC: a dynamic logic of delegation and cooperation. The logical foundation of DCL-PC is CL-PC, a logic for reasoning about cooperation in which the powers of agents and coalitions of agents stem from a distribution of atomic Boolean variables to individual agents - the choices available to coalitions in CL-PC correspond to the possible truth assignments to the propositions they control. The basic modal constructs of CL-PC are of the form "coalition C can cooperate to bring about φ". DCL-PC extends CL-PC with dynamic logic modalities in which atomic programs are of the form "agent i gives proposition p to agent j". By combining these dynamic delegation operators with cooperation modalities, it is possible to reason about delegation and how it affects the power structure within a society. We give two alternative semantics for the logic, (a "direct" semantics, in which we directly represent the distributions of atomic propositions to agents, and a more conventional Kripke semantics), and prove that these semantics are equivalent. We then present a sound and complete axiomatization, and investigate the computational complexity of the model checking and satisfiability problems for DCL-PC.

Playing Cards with Hintikka: An Introduction to Dynamic Epistemic Logic

Abstract: This contribution is a gentle introduction to so-called dynamic epistemic logics, that can describe how agents change their knowledge and beliefs. We start with a concise introduction to epistemic logic, through the example of one, two and finally three players holding cards; and, mainly for the purpose of motivating the dynamics, we also very summarily introduce the concepts of general and common knowledge. We then pay ample attention to the logic of public announcements, wherein agents change their knowledge as the result of, indeed, public announcements. One crucial topic in that setting is that of unsuccessful updates: formulas that become false when announced. The Moore-sentences that were already extensively discussed at the conception of epistemic logic in [15] give rise to such unsuccessful updates. After that, we present a few examples of more complex epistemic updates. Our closing observations are on recent developments that link the ‘standard’ topic of (theory) belief revision [1] to the dynamic epistemic logics introduced here.

Logical implementation of uncertain agents

Abstract: We consider the representation and execution of agents specified using temporal logics. Previous work in this area has provided a basis for the direct execution of agent specifications, and has been extended to allow the handling of agent beliefs, deliberation and multi-agent groups. However, the key problem of uncertainty has not been tackled. Given that agents work in unknown environments, and interact with other agents that may, in turn, be unpredictable, then it is essential for any formal agent description to incorporate some mechanism for capturing this aspect. Within the framework of executable specifications, formal descriptions involving uncertainty must also be executable. The contribution of this paper is to extend executable temporal logic in order to allow the representation and execution of uncertain statements within agents. In particular, we extend the basis of the MetateM temporal framework with a probabilistic belief dimension captured by the recently introduced PFKD45 logic. We provide a description of the extended logic, the translation procedure for formulae in this extended logic to an executable normal form, and the execution algorithm for such formulae. We also outline technical results concerning the correctness of the translation to the normal form and the completeness of the execution mechanism.

Process algebra and constraint programming for modeling interactions in MAS

Abstract: We show how techniques from the realm of concurrent computation can be adapted for modeling the interactions of agents in multi-agent systems. In particular, we introduce a general process-algebraic approach to modeling multiagent systems. Our approach consists of an integration of the process algebras of Communicating Sequential Processes (CSP) and Concurrent Constraint Programming (CCP) for modeling the communication, synchronization and coordination in multiagent systems, including FIPA-style communication primitives and a programming language for group actions in a multi-agent system.

Teams over Time — a Logical Perspective

Abstract: Although the notion of ‘agency’ has always been central to the 50-year old discipline of Artificial Intelligence, the research focus within this field has historically been on isolated, disembodied intelligences. It is only since the early 1980s, and the emergence of the sub-field known as distributed AI, that the emphasis within this community began to change, and focus on cooperative problem-solving and teamwork (Bond and Gasser, 1988).