On the Expressiveness of Pure Mobile Ambients

We consider the Pure Ambient Calculus, which is Cardelli and Gordon's Ambient Calculus (or more precisely its safe version by Levi and Sangiorgi) restricted to its mobility primitives, and we focus on its expressive power. Since it has no form of communication or substitution, we show how these notions can be simulated by mobility and modifications in the hierarchical structure of ambients. As an example, we give an encoding of the synchronous π-calculus into pure ambients and we state an operational correspondence result. In order to simplify the proof and give an intuitive understanding of the encoding, we design an intermediate language: the π-Calculus with Explicit Substitutions and Channels, which is a syntactic extension of the π-calculus with a specific operational semantics.     

On the Expressiveness of Pure Mobile Ambients

We consider the Pure Ambient Calculus, which is Cardelli and Gordon's Ambient Calculus (or more precisely its safe version by Levi and Sangiorgi) restricted to its mobility primitives, and we focus on its expressive power. Since it has no form of communication or substitution, we show how these notions can be simulated by mobility and modifications in the hierarchical structure of ambients. As an example, we give an encoding of the synchronous π-calculus into pure ambients and we state an operational correspondence result. In order to simplify the proof and give an intuitive understanding of the encoding, we design an intermediate language: the π-Calculus with Explicit Substitutions and Channels, which is a syntactic extension of the π-calculus with a specific operational semantics.     

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。     

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.     

移动网可达树

随着计算机技术和网络通信技术的高速发展,对于并发分布式系统,已经提出了进程代数以及Petri网等形式化分析方法。近年来由于移动互联网的出现和快速发展,通过在进程代数中增加移动性得到了pi演算,与此同时,Petri网领域也采用谓词/变迁网、颜色网等构建移动系统模型。但它们仍存在一些不足之处。在此基础上,A.Asperti和N.Busi提出了移动网这一系统模型。移动网是在Petri网的基础上增加了移动性并结合了进程代数的优势得到的,适用于描述和刻画移动计算系统。然而,目前并没有对于移动网相应分析方法的研究。为此开展了移动网模型分析方法的研究,给出了移动网可达树的构造算法,提供了移动网模型可达性分析方法,并对移动车辆电话通信系统实例进行了分析。     

Predicate μ-Calculus for Mobile Ambients

Ambient logics have been proposed to describe properties for mobile agents which may evolve over time as well as space. This paper takes a predicate-based approach to extending an ambient logic with recursion, yielding a predicate μ-calculus in which fixpoint formulas are formed using predicate variables. An algorithm is developed for model checking finite-control mobile ambients against formulas of the logic, providing the first decidability result for model checking a spatial logic with recursion.     

MAX-PLUS ALGEBRA MODELING FOR A PUBLIC TRANSPORT SYSTEM

Abstract

This paper discusses the use of Petri net languages, particularly, its subclass “timed event graph” for modeling a public transport network. The behavior of the network is described by a particular algebraic structure called (max, +) algebra. We show that the modeling of such a network is possible under some hypotheses. We propose a Petri net tool with some conflicts to model this network without taking into account these assumptions. The behavior of this Petri net in (max, +) algebra is presented. An example is given to illustrate our results.     

基于对象Petri网的离散事件系统建模仿真环境(OPMSE)

首先论述了Ｐｅｔｒｉ网和高级Ｐｅｔｒｉ网发展状况,提出了一种高级Ｐｅｔｒｉ网,即对象Ｐｅｔｒｉ网。然后介绍了基于对象Ｐｅｔｒｉ网的离散事件系统建模仿真环境ＯＰＭＳＥ。文中详细介绍了ＯＰＭＳＥ的特点与组成,并对ＯＰＭＳＥ的核心－对象Ｐｅｔｒｉ网（ＯＰＮ）的语法描述进行了重点介绍。     

Fair ambients

Based on an analysis of the capability operators of the Calculus of Mobile Ambients, three fairness principles are proposed to safeguard the interactions of the ambients. The Calculus of Fair Ambient is designed to meet these fairness principles. A labeled transition semantics for the calculus is defined to support structural investigation. The bisimulation theory of the fair ambients is studied and two coincidence results are established. An expressiveness result of the calculus is formally established by proving that it contains the pi calculus as a sub-calculus.     

Ambient Calculus and its Logic in the Calculus of Inductive Constructions

The Ambient Calculus has been recently proposed as a model of mobility of agents in a dynamically changing hierarchy of domains. In this paper, we describe the implementation of the theory and metatheory of Ambient Calculus and its modal logic in the Calculus of Inductive Constructions. We take full advantage of Higher-Order Abstract Syntax, using the Theory of Contexts a fundamental tool for developing formally the metatheory of the object system. Among others, we have successfully proved a set of fresh renamings properties, and formalized the connection between the Theory of Contexts and Gabbay-Pitts' “new” quantifier. As a feedback, we introduce a new definition of satisfaction for the Ambients logic and derive some of the properties originally assumed as axioms in the Theory of Contexts.     

A Petri net-based approach for supporting aspect-oriented modeling

The concept of aspect-orientation allows for modularizing crosscutting concerns as aspect modules. Aspect-orientation originally emerged at the programming level, and has stretched over other development phases now. Among them aspect-oriented modeling (AOM) is a hot topic, and there are many approaches supporting it. Petri net is a good formalism which can provide the foundations for modeling software and simulating its execution, but fails to resolve the problem of crosscutting concerns to support AOM. So, this paper presents an approach which extends the Petri net so as to support the AOM. In this paper, the basic functions of the system are modeled as base net by Petri net, and the crosscutting concerns are modeled as aspect nets. In order to analyze the whole system, woven mechanism is proposed to compose the aspect nets and base net together. The problems about aspect-aspect conflict and conflict relations may exist among the aspect nets matching the shared join point, thus this paper propose solutions to resolve them. The Object Petri net which is an extension of traditional Petri net is also extended so as to support aspect-oriented modeling here.     

A Petri net-based approach for supporting aspect-oriented modeling

The concept of aspect-orientation allows for modularizing crosscutting concerns as aspect modules. Aspect-orientation originally emerged at the programming level, and has stretched over other development phases now. Among them aspect-oriented modeling (AOM) is a hot topic, and there are many approaches supporting it. Petri net is a good formalism which can provide the foundations for modeling software and simulating its execution, but fails to resolve the problem of crosscutting concerns to support AOM. So, this paper presents an approach which extends the Petri net so as to support the AOM. In this paper, the basic functions of the system are modeled as base net by Petri net, and the crosscutting concerns are modeled as aspect nets. In order to analyze the whole system, woven mechanism is proposed to compose the aspect nets and base net together. The problems about aspectaspect conflict and conflict relations may exist among the aspect nets matching the shared join point, thus this paper propose solutions to resolve them. The Object Petri net which is an extension of traditional Petri net is also extended so as to support aspect-oriented modeling here.     

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.     

DEDS对象化高级Petri网模型研究——柔性生产线对象化高级Petri网模型

在加色网基础上,提出一种新的扩展Petri网模型.该模型具以下特点:对进程演化的 有序结构建立偏序集数据抽象,使网络的几何结构与代数运算脱离具体进程特征;使用谓词 集对加入变迁的token进行覆盖,可以集中描述物理事件集的层次逻辑结构;能方便有效地 描述非固定流程生产系统.     

Probabilistic Mobile Ambients

The calculus of Mobile Ambients has been introduced for expressing mobility and mobile computation. In this paper we present a probabilistic version of Mobile Ambients by augmenting the syntax of the original Ambient Calculus with a (guarded) probabilistic choice operator. To allow for the representation of both the probabilistic behaviour introduced through the new probabilistic choice operator and the nondeterminism present in the original Ambient Calculus we use probabilistic automata as the underpinning semantic model. The Ambient logic is a logic for Mobile Ambients that contains a novel treatment of both locations and hidden names. For specifying properties of Probabilistic Mobile Ambients, we extend this logic to specify probabilistic behaviour. In addition, to show the utility of our approach we present an example of a virus infecting a network.     

Incidence calculus: A mechanism for probabilistic reasoning

Mechanisms for the automation of uncertainty are required for expert systems. Sometimes these mechanisms need to obey the properties of probabilistic reasoning. We argue that a purely numeric mechanism, like those proposed so far, cannot provide a probabilistic logic with truth functional connectives. We propose an alternative mechanism, Incidence Calculus, which is based on a representation of uncertainty using sets of points, which might represent situations models or possible worlds. Incidence Calculus does provide a probabilistic logic with truth functional connectives.     

On the Regularity of Petri Net Languages

Petri nets are known to be useful for modeling concurrent systems. Once modeled by a Petri net, the behavior of a concurrent system can be characterized by the set of all executable transition sequences, which in turn can be viewed as a language over an alphabet of symbols corresponding to the transitions of the underlying Petri net. In this paper, we study the language issue of Petri nets from a computational complexity viewpoint. We analyze the complexity of theregularity problem(i.e., the problem of determining whether a given Petri net defines an irregular language or not) for a variety of classes of Petri nets, includingconflict-free,trap-circuit,normal,sinkless,extended trap-circuit,BPP, andgeneralPetri nets. (Extended trap-circuit Petri nets are trap-circuit Petri nets augmented with a specific type ofcircuits.) As it turns out, the complexities for these Petri net classes range from NL (nondeterministic logspace), PTIME (polynomial time), and NP (nondeterministic polynomial time), to EXPSPACE (exponential space). In the process of deriving the complexity results, we develop adecomposition approachwhich, we feel, is interesting in its own right, and might have other applications to the analysis of Petri nets as well. As a by-product, an NP upper bound of the reachability problem for the class of extended trap-circuit Petri nets (which properly contains that of trap-circuit (and hence, conflict-free) and BPP-nets, and is incomparable with that of normal and sinkless Petri nets) is derived.     

Flow-sensitive type systems and the ambient calculus

The Ambient Calculus was developed by Cardelli and Gordon as a formal framework to study issues of mobility and migrant code. Numerous analyses have been developed for numerous variants of that calculus. We take up the challenge of developing, in a type-based setting, a relatively precise “topology” analysis for the original version of the calculus. To compensate for the lack of “co-capabilities” (an otherwise increasingly popular extension), the analysis is flow-sensitive, with the actions of processes being summarized by “behaviors”. A subject reduction property guarantees that for a well-typed process, the location of any ambient is included in what is predicted by its type; additionally it ensures that communicating subprocesses agree on their “topic of conversation”. Based on techniques borrowed from finite automata theory, type checking of type-annotated processes is decidable (though potentially exponential).