Towards a Model of Learning through Communication

Communication is an interactive, complex, structured process involving agents that are capable of drawing conclusions from the information they have available about some real-life situations. Such situations are generally characterized as being imperfect. In this paper, we aim to address learning from the perspective of the communication between agents. To learn a collection of propositions concerning some situation is to incorporate it within one's knowledge about that situation. That is, the key factor in this activity is for the goal agent, where agents may switch role if appropriate, to integrate the information offered with what it already knows. This may require a process of belief revision, which suggests that the process of incorporation of new information should be modeled nonmonotonically. We shall employ for reasoning a three-valued based nonmonotonic logic that formalizes some aspects of revisable reasoning and it is accessible to implementation. The logic is sound and complete. A theorem-prover of the logic has successfully been implemented. Received 3 August 1999 / Revised 17 April 2000 / Accepted 6 May 2000     

Symbolic approximation: an approach to verification in the large

This article describes symbolic approximation, a theoretical foundation for techniques evolved for large-scale verification – in particular, for post hoc verification of the C code in large-scale open-source projects such as the Linux kernel. The corresponding toolset’s increasing maturity means that it is now capable of treating millions of lines of C code source in a few hours on very modest support platforms. In order to explicitly manage the state-space-explosion problem that bedevils model-checking approaches, we work with approximations to programs in a symbolic domain where approximation has a well-defined meaning. A more approximate program means being able to say less about what the program does, which means weaker logic for reasoning about the program. So we adjust the approximation by adjusting the applied logic. That guarantees a safe approximation (one which may generate false alarms but no false negatives) provided the logic used is weaker than the exact logic of C. We choose the logic to suit the analysis.     

Multiagent reasoning with probability,time, and beliefs

Any agent interacting with the real world must be able to reason about uncertainty in the world, about the actions that may occur in the world (either due to the agent or those initiated by other agents), about the (probabilistic) beliefs of other agents, and how these (probabilistic) beliefs are changing over time. In this article, we develop a family of logics that a reasoning agent may use to perform successively more sophisticated types of reasoning in such environments. We also characterize different types of agents. Furthermore, we provide a logic that enables a systems designer (who may have populated an environment with a collection of such autonomous agents) to reason about the system of agents as a whole. © 1995 John Wiley & Sons, Inc.     

Programming Rational Agents in a Modal Action Logic

In this paper we describe a language for reasoning about actions that can be used for modelling and for programming rational agents. We propose a modal approach for reasoning about dynamic domains in a logic programming setting. Agent behavior is specified by means of complex actions which are defined using modal inclusion axioms. The language is able to handle knowledge producing actions as well as actions which remove information. The problem of reasoning about complex actions with incomplete knowledge is tackled and the temporal projection and planning problems is addressed; more specifically, a goal directed proof procedure is defined, which allows agents to reason about complex actions and to generate conditional plans. We give a non-monotonic solution for the frame problem by making use of persistency assumptions in the context of an abductive characterization. The language has been used for implementing an adaptive web-based system.     

Minimal Belief and Negation as Failure in Multi-Agent Systems

We propose an epistemic, nonmonotonic approach to the formalization of knowledge in a multi-agent setting. From the technical viewpoint, a family of nonmonotonic logics, based on Lifschitz's modal logic of minimal belief and negation as failure, is proposed, which allows for formalizing an agent which is able to reason about both its own knowledge and other agents' knowledge and ignorance. We define a reasoning method for such a logic and characterize the computational complexity of the major reasoning tasks in this formalism. From the practical perspective, we argue that our logical framework is well-suited for representing situations in which an agent cooperates in a team, and each agent is able to communicate his knowledge to other agents in the team. In such a case, in many situations the agent needs nonmonotonic abilities, in order to reason about such a situation based on his own knowledge and the other agents' knowledge and ignorance. Finally, we show the effectiveness of our framework in the robotic soccer application domain.     

Logical formalisms for representing bipolar preferences

Bipolar preferences distinguish between negative preferences inducing what is acceptable by complementation and positive preferences representing what is really satisfactory. This article provides a review of the main logics for preference representation. Representing preferences in a bipolar logical way has the advantage of enabling us to reason about them, while increasing their expressive power in a cognitively meaningful way. In the article, we first focus on the possibilistic logic setting and then discuss two other logics: qualitative choice logic and penalty logic. Finally, an application of bipolar preferences querying systems is outlined. © 2008 Wiley Periodicals, Inc.     

On the logic of preference and judgment aggregation

Agents that must reach agreements with other agents need to reason about how their preferences, judgments, and beliefs might be aggregated with those of others by the social choice mechanisms that govern their interactions. The emerging field of judgment aggregation studies aggregation from a logical perspective, and considers how multiple sets of logical formulae can be aggregated to a single consistent set. As a special case, judgment aggregation can be seen to subsume classical preference aggregation. We present a modal logic that is intended to support reasoning about judgment aggregation scenarios (and hence, as a special case, about preference aggregation): the logical language is interpreted directly in judgment aggregation rules. We present a sound and complete axiomatisation. We show that the logic can express aggregation rules such as majority voting; rule properties such as independence; and results such as the discursive paradox, Arrow’s theorem and Condorcet’s paradox—which are derivable as formal theorems of the logic. The logic is parameterised in such a way that it can be used as a general framework for comparing the logical properties of different types of aggregation—including classical preference aggregation. As a case study we present a logical study of, including a formal proof of, the neutrality lemma, the main ingredient in a well-known proof of Arrow’s theorem.     

PROPOSITIONAL DYNAMIC LOGIC FOR REASONING ABOUT FIRST‐CLASS AGENT INTERACTION PROTOCOLS

For agents to fulfill their potential of being intelligent and adaptive, it is useful to model their interaction protocols as executable entities that can be referenced, inspected, composed, shared, and invoked between agents, all at runtime. We use the term first‐class protocol to refer to such protocols. Rather than having hard‐coded decision‐making mechanisms for choosing their next move, agents can inspect the protocol specification at runtime to do so, increasing their flexibility. In this article, we show that propositional dynamic logic (PDL) can be used to represent and reason about the outcomes of first‐class protocols. We define a proof system for PDL that permits reasoning about recursively defined protocols. The proof system is divided into two parts: one for reasoning about terminating protocols, and one for reasoning about nonterminating protocols. We prove that proofs about terminating protocols can be automated, while proofs about nonterminating protocols are unable to be automated in some cases. We prove that, for a restricted class of nonterminating protocols, proofs about them can be transformed to proofs about terminating protocols, making them automatable.     

Specifying real-time properties with metric temporal logic

This paper is motivated by the need for a formal specification method for real-time systems. In these systemsquantitative temporal properties play a dominant role. We first characterize real-time systems by giving a classification of such quantitative temporal properties. Next, we extend the usual models for temporal logic by including a distance function to measure time and analyze what restrictions should be imposed on such a function. Then we introduce appropriate temporal operators to reason about such models by turning qualitative temporal operators into (quantitative) metric temporal operators and show how the usual quantitative temporal properties of real-time systems can be expressed in this metric temporal logic. After we illustrate the application of metric temporal logic to real-time systems by several examples, we end this paper with some conclusions.Part of this research has been performed at the Eindhoven University of Technology when the author was working in ESPRIT project 937: Debugging and Specification of Ada Real-Time Embedded Systems (DESCARTES).     

Reasoning about coalitional agency and ability in the logics of “bringing-it-about”

The logics of “bringing-it-about” have been part of a prominent tradition for the formalization of individual and institutional agency. They are the logics to talk about what states of affairs an acting entity brings about while abstracting away from the means of action. Elgesem’s proposal analyzes the agency of individual agents as the goal-directed manifestation of an individual ability. It has become an authoritative modern reference. The first contribution of this paper is to extend Elgesem’s logic of individual agency and ability to coalitions. We present a general theory and later propose several possible specializations. As a second contribution, we offer algorithms to reason with the logics of bringing-it-about and we analyze their computational complexity.     

Free will - even for robots

Human free will is a product of evolution and contributes to the success of the human animal. Useful robots will also require free will of a similar kind, and we will have to design it into them. Free will is not an all-or-nothing thing. Some agents have more free will, or free will of different kinds, than others, and we will try to analyse this phenomenon. Our objectives are primarily technological, i.e. to study what aspects of free will can make robots more useful, and we will not try to console those who find determinism distressing. We distinguish between having choices and being conscious of these choices; both are important, even for robots, and consciousness of choices requires more structure in the agent than just having choices and is important for robots. Consciousness of free will is therefore not just an epiphenomenon of structure serving other purposes. Free will does not require a very complex system. Young children and rather simple computer systems can represent internally ‘I can, but I won't’ and behave accordingly. Naturally I hope this detailed design stance will help understand human free will. It takes the compatibilist philosophical position. There may be some readers interested in what the paper says about human free will and who are put off by logical formulas. The formulas are not important for the arguments about human free will; they are present for people contemplating AI systems using mathematical logic. They can skip the formulas, but the coherence of what remains is not absolutely guaranteed.     

Analysis of Authentication Protocols in Agent-Based Systems Using Labeled Tableaux

The study of multiagent systems (MASs) focuses on systems in which many intelligent agents interact with each other using communication protocols. For example, an authentication protocol is used to verify and authorize agents acting on behalf of users to protect restricted data and information. After authentication, two agents should be entitled to believe that they are communicating with each other and not with intruders. For specifying and reasoning about the security properties of authentication protocols, many researchers have proposed the use of belief logics. Since authentication protocols are designed to operate in dynamic environments, it is important to model the evolution of authentication systems through time in a systematic way. We advocate the systematic combinations of logics of beliefs and time for modeling and reasoning about evolving agent beliefs in MASs. In particular, we use a temporal belief logic called TML$^{+}$ for establishing trust theories for authentication systems and also propose a labeled tableau system for this logic. To illustrate the capabilities of TML$^{+}$, we present trust theories for several well-known authentication protocols, namely, the Lowe modified wide-mouthed frog protocol, the amended Needham–Schroeder symmetric key protocol, and Kerberos. We also show how to verify certain security properties of those protocols. With the logic TML$^{+}$ and its associated modal tableaux, we are able to reason about and verify authentication systems operating in dynamic environments.      

Reasoning about plan revision in BDI agent programs

Facilities for handling plan execution failures are essential for agents which must cope with the effects of nondeterministic actions, and some form of failure handling can be found in most mature agent programming languages and platforms. While such features simplify the development of more robust agents, they make it hard to reason about the execution of agent programs, e.g., to verify their correctness. In this paper, we present an approach to the verification of agent programs which admit exceptional executions. We consider executions of the BDI-based agent programming language 3APL in which plans containing non-executable actions can be revised using plan revision rules, and present a logic for reasoning about normal and exceptional executions of 3APL programs. We provide a complete axiomatization for the logic and, using a simple example, show how to express properties of 3APL programs as formulas of the logic.     

A Dynamic Logic of Agency II: Deterministic $${\mathcal{DLA}}$$ , Coalition Logic,and Game Theory

We continue the work initiated in Herzig and Lorini (J Logic Lang Inform, in press) whose aim is to provide a minimalistic logical framework combining the expressiveness of dynamic logic in which actions are first-class citizens in the object language, with the expressiveness of logics of agency such as STIT and logics of group capabilities such as CL and ATL. We present a logic called DDLA{\mathcal{DDLA}} (Deterministic Dynamic logic of Agency) which supports reasoning about actions and joint actions of agents and coalitions, and agentive and coalitional capabilities. In DDLA{\mathcal{DDLA}} it is supposed that, once all agents have selected a joint action, the effect of this joint action is deterministic. In order to assess DDLA{\mathcal{DDLA}} we prove that it embeds Coalition Logic. We then extend DDLA{\mathcal{DDLA}} with modal operators for agents’ preferences, and show that the resulting logic is sufficiently expressive to capture the game-theoretic concepts of best response and Nash equilibrium.     

Automata for Epistemic Temporal Logic with Synchronous Communication

We suggest that developing automata theoretic foundations is relevant for knowledge theory, so that we study not only what is known by agents, but also the mechanisms by which such knowledge is arrived at. We define a class of epistemic automata, in which agents’ local states are annotated with abstract knowledge assertions about others. These are finite state agents who communicate synchronously with each other and information exchange is ‘perfect’. We show that the class of recognizable languages has good closure properties, leading to a Kleene-type theorem using what we call regular knowledge expressions. These automata model distributed causal knowledge in the following way: each agent in the system has a partial knowledge of the temporal evolution of the system, and every time agents synchronize, they update each other’s knowledge, resulting in a more up-to-date view of the system state. Hence we show that these automata can be used to solve the satisfiability problem for a natural epistemic temporal logic for local properties. Finally, we characterize the class of languages recognized by epistemic automata as the regular consistent languages studied in concurrency theory.     

Specification of communicating processes: temporal logic versus refusals-based refinement

In this paper we consider the relationship between refinement-oriented specification and specifications using a temporal logic. We investigate the extent to which one can check whether a program in a process algebra, such as Communicating Sequential Processes (CSP), satisfies a temporal logic specification using a refinement-based model checker, such as FDR. We consider what atomic formulae are appropriate in a temporal logic for specifying communicating processes, in particular where one wants to talk about the availability of events. We then show that, perhaps surprisingly, the standard stable failures model is not adequate for capturing specifications in such a logic: instead the refusal traces model must be used. We formalise the logic by giving it a semantics in this model. We show that the temporal operators eventually and until, and negation, cannot, in general, be tested for via simple refinement checks. For the remaining fragment of the logic, we present a translation into simple refinement checks. Finally, we show that refusal traces equivalence is characterised by a slightly augmented version of that fragment. M. J. Butler     

RAO logic for multiagent framework

In this paper,we deal with how agents reason about knowledge of others in multiagent system.We first present a knowledge representation framework called reasoning about others(RAO) which is designed specifically to represent concepts and rules used in reasoning about knowledge of others.From a class of sentences usually taken by people in daily life to reason about others,a rule called position exchange principle(PEP)is abstracted.PEP is described as an axiom scheme in RAO and regarded as a basic rule for agents to reason about others,and further it has the similar form and role to modus ponens and(K) axion of knowledge logic.The relationship between speech acts and common sense is also discussed which is necessary for RAO.Based on ideas from situation calculus,this relationship is characterized by an axiom schema in RAO.Our theories are also demonstrated by an example.     

On logic programs that do not fail

This paper investigates the advantages of reasoning on logic programs and queries that have only successful derivations. We consider an extension of the logic programming paradigm that combines guarded clauses and delay declarations. The main contribution of this paper consists of some general conditions for a class of programs and queries which imply that successful derivations only are present. A few practical instances of the method are studied, and their applicability demonstrated. The general conditions are derived extending proof methods originally developed for Prolog's programs. From the point of view of parallelism, the method is able to reason about termination (with success) of pipeline parallel executions of programs. In particular, we show some examples of parallelization of terminating Prolog programs. Moreover, from the point of view of nondeterminism, don't care nondeterminism can be safely adopted for the class of programs that have only successfull derivations.     

Deontic logic in the representation of law: Towards a methodology

There seems to be no clear consensus in the existing literature about the role of deontic logic in legal knowledge representation — in large part, we argue, because of an apparent misunderstanding of what deontic logic is, and a misplaced preoccupation with the surface formulation of legislative texts. Our aim in this paper is to indicate, first, which aspects of legal reasoning are addressed by deontic logic, and then to sketch out the beginnings of a methodology for its use in the analysis and representation of law.The essential point for which we argue is that deontic logic — in some form or other —needs to be taken seriously whenever it is necessary to make explicit, and then reason about, the distinction between what ought to be the case and what is the case, or as we also say, between the ideal and the actual. We take the library regulations at Imperial College as the main illustration, and small examples from genuinely legal domains to introduce specific points. In conclusion, we touch on the role of deontic logic in the development of the theory of normative positions.Deontic logic and the theory of normative positions are of relevance to legal knowledge representation, but also to the analysis and. representation of normative systems generally. The emphasis of the paper is on legal knowledge representation, but we seek to place the discussion within the context of a broader range of issues concerning the role of deontic logic in Computer Science.