移动计算形式理论分析与研究

移动计算是在网络技术发展中涌现出的一种新计算范型,文章旨在从形式抽象的角度来认识移动计算的本质特点,文中分析了网络计算平台的综合特征,总结了移动计算范型的曲型特征,重点介绍了有代表性的移动计算形式模型和方法,包括进程代数类的π－演算、环境演算和Ｓｅａｌ演算、时序逻辑类的移动Ｕｎｉｔｙ,以及Ａｃｔｏｒ扩充模型,针对每个模型或方法,分析了位置、移动等概念在模型中的刻画,以及各自的交互、动态配置重构和资     

类型化移动资源

在移动资源演算(MR)中发现了一种干扰现象,称为直接访问干扰,该现象比移动灰箱演算(MA)中的墙干扰现象更具破坏力,因为在MR中恶意的环境或上下文可以不受限制地访问进程内部的敏感资源.因而该干扰问题当被视为一种程序运行错误.为了控制直接干扰现象,提出了一种MR的变体:安全移动资源演算(SR).它使用了一种类型系统来避免所有的直接访问干扰的发生.基于该研究,MA中的强干扰现象实际上是直接访问干扰的一种特殊形式,自然地,在SR中也得到了相应的控制.最后给出一些用例,说明如何使用新设计的演算系统,以及它的健壮性.     

一种改进的安全环境演算及其行为等价关系研究

移动计算是在网络技术发展过程中涌现出来的一种新的分布计算范型．移动环境演算是一种广为使用的描述移动计算的形式化模型．安全环境演算为每个动作原语增加了一个相应的协动作原语，从而解决了强干扰问题．然而，SA的语法定义在直觉上并不能很好地描述out原语的协动作，同时其代数性质也存在一些缺陷．针对这些问题，一方面调整了SA的归约关系，将出入动作的语义统一在“进入时检查”这一约定之下，使其更符合直觉含义．在此基础上，通过采用Honda—Yoshida的技术，定义开接口互模拟等价关系，修正了SA代数性质上的缺陷，并通过一个防火墙的饲子说明了改进的安全环境演算及其行为等价关系的合理性．     

移动Agent计算理论和形式化方法研究

研究了移动Agent计算的基础理论和形式化方法,包括π-演算、多态π演算、高阶π演算和环境演算等4种进程代数理论,分析了它们如何对Agent、位置、移动、通信、安全、命名、资源控制和动态配置等移动Agent计算的基本概念进行刻画,并比较了它们刻画移动Agent计算的优缺点,在此基础上提出了移动概念的分类与抽象.     

BREW及其应用开发

BREW是在移动数据增值应用开发领域出现的新技术。对BREW技术及其应用开发环境进行了介绍，对基于BREW环境进行新一代无线移动数据应用开发的方法和过程进行了深入探讨，并指出了开发中应注意解决的问题。     

EMDB技术在基于WLAN的餐饮管理系统中的研究与应用

移动数据库技术是支持移动计算环境的分布式数据库技术，在移动计算环境中有许多重要应用。对嵌入式移动数据库的几种关键技术——数据广播技术，复制缓存技术、移动事务处理技术分别进行了分析，通过嵌入式移动数据库在基于无线局域网的餐饮管理系统中的应用实例探讨了移动数据库的应用前景。     

移动分布式系统——技术现状和发展

系统地分析了移动分布式系统的技术、研究工作及关键问题的现状，在介绍基本概念和移动网络环境特性的基础上，按照研究层次、应用类型和关键问题等不同角度，对研究工作进行了深入的分析，并详细讨论了移动分布式系统的研究现状。随后，列举了一些有代表性的系统和相应技术特点。文章最后指出了移动分布式系统的研究发展方向。     

移动事务处理技术研究进展

在移动计算环境中,移动用户能够随时随地访问所需的信息,移动计算环境应提供相应的事务处理能力。但是,由于移动计算环境的限制,移动事务不完全等同于传统事务。提出了移动事务的概念和特征,分析了移动事务处理的目标,讨论了典型的移动事务模型,并对这些移动事务处理模型进行了比较和总结。     

移动界程演算理论及应用研究综述

移动界程演算通过界程这一核心概念来表达有边界的计算场所,并提供界程移动,认证和授权等能力从最基础层次刻画移动计算的本质,成为了移动计算系统形式化理论和应用领域内的重要研究分支。对移动界程演算的理论及应用方面的研究和发展进行了概述,对移动界演算的扩展语义和代数性质的分析方法、移动界演算的空间逻辑和模型检测算法以及移动界程在计算系统建模方面应用现状进行了整理和分析,并对该领域未来进一步研究的方向进行了展望。     

移动环境下基于移动代理的应用框架设计

随着网络技术的发展和移动设备的普及，用户希望能随时随地对资源进行访问。但是，由于移动网络连接带宽低且移动单元本身资源贫乏，移动环境为分布应用开发提出了新的挑战。移动代理技术以其节省带宽、异步性等特征，为移动计算提供了良好的解决方案。本文首先讨论了移动代理系统的设计，然后提出一个基于移动代理的移动应用框架
架，最后给出了相应的应用实例。     

Types for the Ambient Calculus

The ambient calculus is a concurrent calculus where the unifying notion of ambient is used to model many different constructs for distributed and mobile computation. We study a type system that describes several properties of ambient behavior. The type system allows ambients to be partitioned in disjoint sets (groups), according to the intended design of a system, in order to specify both the communication and the mobility behavior of ambients.     

Ambient演算的数据流分析方法及其实现

针对Ambient演算的定义，提出了Ambient演算语法结构树的概念，并且给出一个基于Ambient语法结构树的Ambient演算的数据流分析方法及其实现。为深入研究Ambient演算的性质和应用提供了分析手段。     

A formal role-based access control model for security policies in multi-domain mobile networks

Mobile users present challenges for security in multi-domain mobile networks. The actions of mobile users moving across security domains need to be specified and checked against domain and inter-domain policies. We propose a new formal security policy model for multi-domain mobile networks, called FPM-RBAC, Formal Policy Model for Mobility with Role Based Access Control. FPM-RBAC supports the specification of mobility and location constraints, role hierarchy mapping, inter-domain services, inter-domain access rights and separation of duty. Associated with FPM-RBAC, we also present a formal security policy constraint specification language for domain and inter-domain security policies. Formal policy constraint specifications are based on ambient logic and predicate logic. We also use ambient calculus to specify the current state of a mobile network and actions within security policies for evaluation of access requests according to security policies. A novel aspect of the proposed policy model is the support for formal and automated analysis of security policies related to mobility within multiple security domains.     

On the expressive power of movement and restriction in pure mobile ambients

Pure mobile ambients is a process calculus suitable to focus on issues related to mobility, abstracting away from aspects concerning process communication. However, it incorporates name restriction (i.e. the (νn) binder) and ambient movement (i.e. the in and out capabilities) that can be seen as characteristics adapted, or directly borrowed, from the tradition of communication-based process calculi. For this reason, we retain that it is worth to investigate whether or not these features can be removed from pure mobile ambients without losing expressive power.To this aim, we consider two variants of pure mobile ambients which differ in the way infinite processes can be defined; the former exploits process replication, while the latter is more general and permits recursive process definition. We analyse whether or not the elimination of ambient movement and/or name restriction reduces the expressive power of these two calculi, using the decidability of process termination as a yardstick. We prove that name restriction can be removed from both calculi without reducing the expressive power. On the other hand, the elimination of both ambient movement and name restriction strictly reduces the expressive power of both calculi. As far as the elimination of only ambient movement is concerned, we prove an interesting discrimination result: process termination is undecidable under recursive process definition, while it turns out to be decidable under process replication.     

Modelling the Security of Smart Cards by Hard and Soft Types for Higher-Order Mobile Embedded Resources

We provide a type system inspired by affine intuitionistic logic for the calculus of Higher-Order Mobile Embedded Resources (Homer), resulting in the first process calculus combining affine linear (non-copyable) and non-linear (copyable) higher-order mobile processes, nested locations, and local names. The type system guarantees that linear resources are neither copied nor embedded in non-linear resources during computation.We exemplify the use of the calculus by modelling a simplistic e-cash Smart Card system, the security of which depends on the interplay between (linear) mobile hardware, embedded (non-linear) mobile processes, and local names. A purely linear calculus would not be able to express that embedded software processes may be copied. Conversely, a purely non-linear calculus would not be able to express that mobile hardware processes cannot be copied.     

Splitting Mobility and Communication in Boxed Ambients

Stemming from our previous work on BACI, a boxed ambient calculus with communication in- terfaces, we define a new calculus that further enhances communication mechanisms and mobility control by introducing multiple communication ports, access control lists, and port hiding.The development of the calculus is mainly focused on three objectives: separation of concerns between mobility and communication, fine-grained controls, and locality. Communication primi- tives use ports to establish communication channels between ambients, while ambient names are only used for mobility. In order to achieve a better control over mobility, the calculus includes co-capabilities à la Safe Ambients, but with the addition of access control lists. These lists contain the names of the ambients that are allowed to enter or exit the ambient with that co-capability.The resulting calculus not only provides more flexibility and expressiveness than Boxed Ambients, but also enables simpler implementations using more powerful constructs for communication and mobility. We establish the basic meta-theory of the calculus by providing rules for type safety and showing that typing is preserved during execution.     

Validating firewalls using flow logics

The ambient calculus is a calculus of computation that allows active processes to communicate and to move between sites. A site is said to be a protective firewall whenever it denies entry to all attackers not possessing the required passwords. We devise a computationally sound test for validating the protectiveness of a proposed firewall and show how to perform the test in polynomial time. The first step is the definition of a flow logic for analysing the flow of control in mobile ambients; it amounts to a syntax-directed specification of the acceptability of a control flow estimate. The second step is to define a hardest attacker and to determine whether or not there exists a control flow estimate that shows the inability of the hardest attacker to enter; if such an estimate exists, then none of the infinitely many attackers can enter unless they contain at least one of the passwords, and consequently the firewall cannot contain any trap doors.     

远程诊断系统中两个关键问题的代数建模

基于网络的远程监测诊断系统是一个复杂的系统,其实施需要进行理性的建模分析.针对基于网络的远程监测诊断系统的实现和分析问题,利用了π演算以及δπ演算这一高度抽象的适于移动分布计算模式的代数建模工具,完成了基于网络的远程监测诊断系统的两个诊断特征问题：移动诊断和群组诊断的建模.建模结果表明δπ演算能很好地表达基于网络的远程监测诊断系统的这两个特征问题.     

Interaction in Time and Space

Distributed π-calculus and ambient calculus are extended with timers which may trigger timeout recovery processes. Timers provide a useful notion of relative time with respect to the interaction in a distributed system. The rather flat notion of space in timed distributed π-calculus is improved by considering a hierarchical representation of space in timed mobile ambients. Some basic results are proven, making sound both formal approaches. An easily understood example is used for both extensions, showing how it is possible to describe a non-monotonic behaviour and use a decentralized control to coordinate the interacting components in time and space.     

The Calculus of Context-aware Ambients

We present the Calculus of Context-aware Ambients (CCA in short) for the modelling and verification of mobile systems that are context-aware. This process calculus is built upon the calculus of mobile ambients and introduces new constructs to enable ambients and processes to be aware of the environment in which they are being executed. This results in a powerful calculus where both mobility and context-awareness are first-class citizens. We present the syntax and a formal semantics of the calculus. We propose a new theory of equivalence of processes which allows the identification of systems that have the same context-aware behaviours. We prove that CCA encodes the π-calculus which is known to be a universal model of computation. Finally, we illustrate the pragmatics of the calculus through many examples and a real-world case study of a context-aware hospital bed.