J.-J. Ch. Meyer

Epistemic Logic for AI and Computer Science: Contents

From the Publisher: Epistemic logic has grown from its philosophical beginnings to find diverse applications in computer science as a means of reasoning about the knowledge and belief of agents. This book, based on courses taught at universities and summer schools, provides a broad introduction to the subject; many exercises are included as well as their solutions. After presenting the necessary apparatus from mathematics and logic, the authors consider applications in the areas of common knowledge, distributed knowledge, explicit and implicit belief.

Epistemic Logic for AI and Computer Science: Frontmatter

From the Publisher: Epistemic logic has grown from its philosophical beginnings to find diverse applications in computer science as a means of reasoning about the knowledge and belief of agents. This book, based on courses taught at universities and summer schools, provides a broad introduction to the subject; many exercises are included as well as their solutions. After presenting the necessary apparatus from mathematics and logic, the authors consider applications in the areas of common knowledge, distributed knowledge, explicit and implicit belief.

A logical approach to the dynamics of commitments

Abstract In this paper we present a formalisation of motivational attitudes, the attitudes that are the driving forces behind the actions of agents. We consider the statics of these attitudes both at the assertion level, i.e., ranging over propositions, and at the practition 2 level, i.e., ranging over actions, as well as the dynamics of these attitudes, i.e., how they change over time. Starting from an agents wishes, which form the primitive, most fundamental motivational attitude, we define its goals as induced by those wishes that do not yet hold, i.e., are unfulfilled, but are within the agents practical possibility to bring about, i.e., are implementable for the agent. Among these unfulfilled, implementable wishes the agent selects those that qualify as its goals. Based on its knowledge on its goals and practical possibilities, an agent may make certain commitments. In particular, an agent may commit itself to actions that it knows to be correct and feasible to bring about some of its known goals. As soon as it no longer knows its commitments to be useful, i.e., leading to fulfillment of some goal, and practically possible, an agent is able to undo these commitments. Both the act of committing as well as that of undoing commitments is modelled as a special model-transforming action in our framework, which extends the usual state-transition paradigm of Propositional Dynamic Logic. In between making and undoing commitments, an agent is committed to all the actions that are known to be identical for all practical purposes to the ones in its agenda. By modifying the agents agenda during the execution of actions in a straightforward way, it is ensured that commitments display an intuitively acceptable behaviour with regard to composite actions.

A verification framework for agent programming with declarative goals

Abstract A long and lasting problem in agent research has been to close the gap between agent logics and agent programming frameworks. The main reason for this problem of establishing a link between agent logics and agent programming frameworks is identified and explained by the fact that agent programming frameworks have hardly incorporated the concept of a declarative goal. Instead, such frameworks have focused mainly on plans or goals-to-do instead of the end goals to be realised which are also called goals-to-be. In this paper, the programming language GOAL is introduced which incorporates such declarative goals. The notion of a commitment strategy—one of the main theoretical insights due to agent logics, which explains the relation between beliefs and goals—is used to construct a computational semantics for GOAL. Finally, a proof theory for proving properties of GOAL agents is introduced. Thus, the main contribution of this paper, rather than the language GOAL itself, is that we offer a complete theory of agent programming in the sense that our theory provides both for a programming framework and a programming logic for such agents. An example program is proven correct by using this programming logic.

The role of deontic logic in the specification of information systems

In this paper we discuss the role that deontic logic plays in the specification of information systems, either because constraints on the systems directly concern norms or, and even more importantly, system constraints are considered ideal but violable (so-called `soft? constraints). To overcome the traditional problems with deontic logic (the so-called paradoxes), we first state the importance of distinguishing between ought-to-be and ought-to-do constraints and next focus on the most severe paradox, the so-called Chisholm paradox, involving contrary-to-duty norms. We present a multi-modal extension of standard deontic logic (SDL) to represent the ought-to-be version of the Chisholm set properly. For the ought-to-do variant we employ a reduction to dynamic logic, and show how the Chisholm set can be treated adequately in this setting. Finally we discuss a way of integrating both ought-to-be and ought-to-do reasoning, enabling one to draw conclusions from ought-to-be constraints to ought-to-do ones, and show by an example the use(fulness) of this.

A Modal Approach to Intentions, Commitments and Obligations: Intention plus Commitment yields Obligation

In this paper we introduce some new operators that make it possible to reason about decisions and commitments to do actions. In our framework, a decision leads to an intention to do an action. The decision in itself does not change the state of the world; a commitment to actually perform the intended action changes the deontic state of the world such that the intended action becomes obligated. Of course, the obligated action may never actually occur. In our semantic structure, we use static (ough-to-be) and dynamic (ought-to-do) obligation operators. The static operator resembles the classical conception of obligation as truth in ideal worlds, except that it takes the current state as well as the past history of the world into account. This is necessary because it allows us to compare the way a state is actually reached with the way we committed ourselves to reach it. We show that some situations that could formerly not be expressed easily in deontic logic can be described in a natural way using the extended logic described in this paper.

Actions that make you change your mind

In this paper we study the dynamics of belief from an agent-oriented, semantics-based point of view. In a formal framework used to specify and to analyze rational agents, we define actions that model three well-known changes of belief, viz. expansions, contractions and revisions. We define both the opportunity for and the result of these belief-changing actions. To define the semantics of the contraction action we introduce selection functions. These functions pick out a set of states that is to be added to the set of doxastic alternatives of an agent, thereby contracting its set of beliefs. The action that models belief revisions is defined as the sequential composition of a contraction and an expansion in a way suggested by the Levi-identity. We show that these belief-changing actions are defined in an intuitively acceptable, reasonable way by proving that the AGM postulates for belief changes are validated.

A Logical Model for Commitment and Argument Network for Agent Communication

In this paper we present a semantics for our approach based on social commitments (SCs) and arguments for conversational agents. More precisely, we propose a logical model based on CTL* and on dynamic logic (DL). Called Commitment and Argument Network, our formal framework based on this approach uses three basic elements: SCs, actions that agents apply to these SCs and arguments that agents use to support their actions. The advantage of this logical model is to bring together all these elements and the relations existing between them within the same framework. Our semantics makes it possible to represent the dynamics of agent communication. It also allows us to establish the important link between SCs as a deontic concept and arguments. CTL* enables us to express the temporal characteristics of SCs and arguments. DL enables us to capture the actions that agents are committed to achieve.

MAKING SOME ISSUES OF IMPLICIT KNOWLEDGE EXPLICIT

We discuss issues of expressibility and completeness of the logic of implicit knowledge (I) and “everybody’s knowledge” (E), as introduced in a system with a number m of epistemic agents by Halpern & Moses. The operator E is defined as a conjunction and corresponds semantically to the union of the m accessibility relations. Dually, the operator I is semantically associated with an intersection, but it is, surprisingly, not equivalent with a disjunction. From the view of Kripke structures there is a related asymmetry: although union can be modally defined, intersection cannot! We discuss consequences (in terms of (in)expressibility, correspondence and completeness) of this property for the epistemic logic under consideration and also present an extension of modal logic in which intersection is expressible.

Issues in Multiagent System Development

Methodologies for multiagent system development should assist the developer in making decisions about those aspects of the analysis, design and implementation, that are crucial for multiagent systems, namely, social and cognitive concepts (e.g. norms and goals). In this paper, we review existing agent-oriented methodologies. We conclude that there is a big gap between the analysis and design models and the implementation. We identify some open issues for multiagent system development. We introduce our vision of a development methodology for multiagent systems, based on the OperA analysis models and the agent-oriented programming language 3APL.