多Agent系统中的常识和分布式知识

Agent的形式化研究已成为人工智能、哲学逻辑和计算语言学共同关心的重要课题,有着广泛的应用。逻辑学的理论为人工智能的发展提供了有力的工具。介绍了Agent系统设计的逻辑学基础,以及模态逻辑和认知逻辑,在此基础之上重点介绍了多Agent系统中的常识和分布式知识。     

一种分析电子商务协议的知识与信念模型

针对现阶段电子商务协议形式化分析的处理比较混乱、表述精确度不高且通用性较差、存在一些不合理的假设等问题,运用现代模态逻辑理论,结合知识与信念,提出了一种分析电子商务协议的模型:知识与信念模型。该模型主要包含安全环境、知识集、信念集、能力集、切入点和知识化等因素。知识与信念模型很好地解决了上述问题,能够细致、精准地对各种电子商务协议进行形式化描述,并为不同的分析方法提供了模型支持。     

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.     

一种Web服务组合的认知模型检测方法

由于Web服务及其协同的动态性,开放多变的互联网运行环境,以及松耦合的服务开发模式所导致的开发和运行过程不确定性,使得Web服务组合的正确性和可靠性等可信性质难以得到保证.将Web服务组合抽象为多主体系统,提出业务流程执行语言BPEL的形式模型BSTS,设计并实现了从BPEL到BSTS的B2S转化算法,以及从BSTS到多主体系统模型检测工具MCMAS输入语言ISPL的S2I转化算法,从而实现Web服务组合的自动形式化建模,使得我们不仅可以验证Web服务组合的时态逻辑规范,而且还可以验证认知与合作等多主体系统特有的逻辑规范.我们实现了相关的模型检测工具原型MCWS,并用其对一个贷款核准服务实例进行建模和验证,实验结果显示了MCWS的有效性.     

Model Checking Russian Cards

We implement a specific protocol for bit exchange among card-playing agents in three different state-of-the-art epistemic model checkers and compare the results.     

On automatic verification of self-stabilizing population protocols

The population protocol model has emerged as an elegant computation paradigm for describing mobile ad hoc networks, consisting of a number of mobile nodes that interact with each other to carry out a computation. The interactions of nodes are subject to a fairness constraint. One essential property of population protocols is that all nodes must eventually converge to the correct output value (or configuration). In this paper, we aim to automatically verify self-stabilizing population protocols for leader election and token circulation in the Spin model checker. We report our verification results and discuss the issue of modeling strong fairness constraints in Spin.     

Knowledge Condition Games

Understanding the flow of knowledge in multi-agent protocols is essential when proving the correctness or security of such protocols. Current logical approaches, often based on model checking, are well suited for modeling knowledge in systems where agents do not act strategically. Things become more complicated in strategic settings. In this paper we show that such situations can be understood as a special type of game – a knowledge condition game – in which a coalition “wins” if it is able to bring about some epistemic condition. This paper summarizes some results relating to these games. Two proofs are presented for the computational complexity of deciding whether a coalition can win a knowledge condition game with and without opponents (Σ₂P-complete and NP-complete respectively). We also consider a variant of knowledge condition games in which agents do not know which strategies are played, and prove that under this assumption, the presence of opponents does not affect the complexity. The decision problem without opponents is still NP-complete, but requires a different proof.Sieuwert van Otterloo thanks the Institute for Logic, Language and Information in Amsterdam for its hospitality during the period that this paper was finalized.     

多智体系统时序认知规范的SPIN模型检测

SPIN模型检测器主要用来检测线性时序逻辑描述的规范,而多智体系统的规范采用时序认知逻辑描述比较方便。本文着重讨论了如何利用SPIN模型检测线性时序认知逻辑的方法,根据局部命题的理论,将模型检测知识算子和公共算子表述的规范规约为模型检测线性时序逻辑的问题,从而使SPIN的检测功能由线性时序逻辑扩充到线性时序认知逻辑。本文通过一个RPC协议分析实例来说明模型检测线性时序认知逻辑的方法。     

Argumentation and the Dynamics of Warranted Beliefs in Changing Environments

One of the most difficult problems in Multi-Agent Systems (MAS) involves representing the knowledge and beliefs of an agent which performs its tasks in a dynamic environment. New perceptions modify this agent’s current knowledge about the world, and consequently its beliefs about it also change. Such a revision and update process should be performed efficiently by the agent, particularly in the context of real-time constraints. In the last decade argumentation has evolved as a successful approach to formalize defeasible, commonsense reasoning, gaining wide acceptance in the MAS community by providing tools for designing and implementing features, which characterize reasoning capabilities in rational agents. In this paper we present a new argument-based formalism specifically designed for representing knowledge and beliefs of agents in dynamic environments, called Observation-based Defeasible Logic Programming (ODeLP). A simple but effective perception mechanism allows an ODeLP-based agent to model new incoming perceptions, and modify the agent’s knowledge about the world accordingly. In addition, in order to improve the reactive capabilities of ODeLP-based agents, the process of computing beliefs in a changing environment is made computationally attractive by integrating a “dialectical database” with the agent’s program, providing pre-compiled information about previous inferences. We present algorithms for managing dialectical databases as well as examples of their use in the context of real-world problems.     

有界模型检测同步多智体系统的时态认知逻辑

提出在同步的多智体系统中验证时态认知逻辑的有界模型检测(bounded model checking,简称BMC)算法.基于同步解释系统语义,在时态逻辑CTL*的语言中引入认知模态词,从而得到一个新的时态认知逻辑ECKL_n.通过引入状态位置函数的方法获得同步系统的智能体知识,避免了为时间域而扩展通常的时态认知模型的状态及迁移关系编码.ECKL_n的时态认知表达能力强于另一个逻辑CTLK.给出该算法的技术细节及正确性证明,并用火车控制系统实例解释算法的执行过程.     

Reasoning about Minimal Knowledge in Nonmonotonic Modal Logics

We study the problem of embedding Halpern and Moses's modal logic of minimal knowledge states into two families of modal formalism for nonmonotonic reasoning, McDermott and Doyle's nonmonotonic modal logics and ground nonmonotonic modal logics. First, we prove that Halpern and Moses's logic can be embedded into all ground logics; moreover, the translation employed allows for establishing a lower bound (3p) for the problem of skeptical reasoning in all ground logics. Then, we show a translation of Halpern and Moses's logic into a significant subset of McDermott and Doyle's formalisms. Such a translation both indicates the ability of Halpern and Moses's logic of expressing minimal knowledge states in a more compact way than McDermott and Doyle's logics, and allows for a comparison of the epistemological properties of such nonmonotonic modal formalisms.     

A heuristic algorithm for distributed control in manufacturing systems

Distributed Problem Solving Networks (DPSN) provide a means for interconnecting intelligent problem solver nodes that can solve only a part of a problem depending on their ability in the problem domain. The decomposition of a problem into subproblems, and the selection of nodes to solve them can be regarded as the generation of an AND/OR tree, and the solution of the problem as a search for a solution tree. Introducing measurements for the cost of a solution tree, we present an algorithm to find one having minimal cost under certain conditions. A Flexible Manufacturing System consisting of a network of flexible workcells is used as an example.     

The Performance of an Efficient Distributed Synchronization and Recovery Algorithm

Concurrency control based on distributed locking introduces delays due to local processing and message communication. With improvements in processor speeds, there is a simultaneous increase in contrast, between these delays. In this study, a new approach has been proposed to reduce delays by enhancing local processing, and reducing the inter-site communication delays. The proposal presents an efficient synchronization algorithm for exchange of precedence in case of a conflict. The technique is efficient in global time-stamp management, and incurs a minimal overall synchronization overhead. A comparative analysis to study the advantages of this approach has shown favourable results. The proposed approach, enhances transaction concurrency and succeeds in lowering the number of inter-site messages.     

Asynchronous Backup and Initialization of a Database Server for Replicated Database Systems

A possibility of a temporary disconnection of database service exists in many computing environments. It is a common need to permit a participating site to lag behind and re-initialize to full recovery. It is also necessary that active transactions view a globally consistent system state for ongoing operations. We present an algorithm for on-the-fly backup and site-initialization. The technique is non-blocking in the sense that failure and recovery procedures do not interfere with ordinary transactions. As a result the system can tolerate disconnection of services and reconnection of disconnected services, without incurring high overheads.     

多主体系统时态认知规范的"On the Fly"模型检测算法研究

时态认知逻辑已被广泛应用于分布式系统和协议的规范描述,模型检测时态认知规范已成为一个新的研究领域,因此着重研讨时态认知规范的“On the Fly”模型检测算法．在“On the Fly”模型检测时态逻辑描述规范的基础上,根据自动机理论、深度优先方法和知识的语义,提出了“On the Fly”模型检测时态认知规范的算法,该算法在模型检测带有知识算子的时态规范时,在找到一个反例之前,往往只需构造系统的部分甚至小部分状态空间,从而避免了时态认知规范的模型检测中内存不足和状态爆炸等问题,实现了“On the Fly”模型检测时态认知规范,并且算法的复杂性是多项式时间的．最后,通过该方法在验证TMN密码协议中的应用来作为一个例子说明该方法的有效性．     

多智能体系统中并发动态知识、信念和肯定性逻辑的研究

将知识、信念和肯定性逻辑从单个智能体扩展到多智能体系统,并且实现了多智能体系统中知识、信念和肯定性逻辑与具有并发动态属性的行为之间的很好结合.以此为基础,提出了多智能体系统中并发动态知识、信念和肯定性逻辑,简称CDKBC逻辑.为了对CDKBC逻辑进行解释,也给出了CDKBC模型,并且讨论了知识、信念和肯定性之间的关系,即知识蕴涵着肯定性,肯定性蕴涵着信念.文中也给出了一个相应的证明系统(即公理系统),证明了该系统是可靠的和完备的,并且证明了系统的有效性问题是EXPTIME完全的.最后论文给出了CDKBC逻辑的实例.     

一种MAS构件知识复用动态演化模型

为提高企业的知识利用效率,增强企业创新能力,针对企业现有知识和系统,提出将企业知识管理的业务逻辑与知识处理事务分开,建立了基于多智能体和构件知识的知识复用模型,设计了知识管理业务逻辑的规则模型和智能体的活动行为模型,讨论了基于多智能体的规则协调模式,有效地支持知识的动态复用和知识使用过程的动态重组,增强知识管理系统的分布式处理能力和规模可扩展能力.在分布式构件库系统中,智能体通过协作联合完成任务要求.每个智能体拥有自己的知识库,并且具备学习能力,能够更新其知识库以保持执行结果的有效性.     

Knowledge organization and its role in representation and interpretation for time-varying data: the ALVEN system

The so-called "first generation" expert systems were rule-based and offered a successful framework for building applications systems for certain kinds of tasks. Spatial, temporal, and causal reasoning, knowledge abstractions, and structuring are among topics of research for "second generation" expert systems. It is proposed that one of the keys for such research is knowledge organization. Knowledge organization determines control structure design, explanation and evaluation capabilities for the resultant knowledge base, and has strong influence on system performance. We are exploring a framework for expert system design that focuses on knowledge organization, for a specific class of input data, namely, continuous, time-varying data (image sequences or other signal forms). Such data are rich in temporal relationships as well as temporal changes of spatial relations, and are thus a very appropriate testbed for studies involving spatio-temporal reasoning. In particular, the representation formalism specifies the semantics of the organization of knowledge classes along the relationships of generalization/specialization, decomposition/aggregation, temporal precedence, instantiation, and expectation-activated similarity. Á hypothesize-and-test control structure is driven by the class organizational principles, and includes several interacting dimensions of search (data-driven, model-driven, goal-driven temporal, and failure-driven search). The hypothesis ranking scheme is based on temporal cooperative computation, with hypothesis "fields of influence" being defined by the hypothesis' organizational relationships. This control structure has proven to be robust enough to handle a variety of interpretation tasks for continuous temporal data. A particular incarnation, the ALVEN system, for left ventricular performance assessment from X-ray image sequences, will be summarized in this paper.