基于项重写系统的联锁系统模型检测方法研究

模型检测方法对安全苛求系统建模的完整性需要一套严谨的方法论与技术,对于验证系统的正确性,具有传统方法无法比拟的优势。提出利用项重写系统建立安全苛求系统模型与验证方法,采用基于项重写系统原理的Maude工具语言,对铁路联锁系统的站场进行形式化建模,通过其语法和语义定义各类约束和离散事件,构架联锁系统属性和行为。在模型建立的基础上,对联锁站场的静态属性和安全属性进行形式化模型验证。结果表明,基于项重写系统的模型检测方法可以较好地应用于实际联锁系统软件的开发,对开发安全苛求系统和模型检测方法的实际应用提供借鉴。     

Logical Semantics for the Rewriting Calculus

The Rewriting Calculus has been proposed as a language for defining term rewriting strategies. Rules are explicitly represented as terms, and are applied explicitly to other terms to transform them. Sets of rules may be applied to (sets of) terms non-deterministically to obtain sets of results. Strategies are implemented as rules which accept other rules as arguments and apply them in certain ways. This paper describes work in progress to strengthen the Rewriting Calculus by giving it a logical semantics. Such a semantics can provide crucial guidance for studying the language and increasing its expressive power. The latter is demonstrated by adding support to the Rewriting Calculus for what we call higher-form rewriting, where rules rewrite other rules. The logical semantics used is based on ordered linear logic. The paper develops the ideas through several examples.     

On the Modularity of Normal Forms in Rewriting

The last open problem regarding the modularity of the fundamental properties of Term Rewriting Systems concerns the property of uniqueness of normal forms w.r.t. reduction (UN^→). In this article we solve this open problem, showing that UN^→is modular for left-linear Term Rewriting Systems. The novel “pile and delete” technique here introduced allows for quite a short proof, and is of independent interest in the study of modular properties. Moreover, we also study the modularity of consistency w.r.t. reduction (CON^→), showing its modularity for left-linear Term Rewriting Systems.     

LARS: A learning algorithm for rewriting systems

Whereas there is a number of methods and algorithms to learn regular languages, moving up the Chomsky hierarchy is proving to be a challenging task. Indeed, several theoretical barriers make the class of context-free languages hard to learn. To tackle these barriers, we choose to change the way we represent these languages. Among the formalisms that allow the definition of classes of languages, the one of string-rewriting systems (SRS) has outstanding properties. We introduce a new type of SRS’s, called Delimited SRS (DSRS), that are expressive enough to define, in a uniform way, a noteworthy and non trivial class of languages that contains all the regular languages, , , the parenthesis languages of Dyck, the language of Lukasiewicz, and many others. Moreover, DSRS’s constitute an efficient (often linear) parsing device for strings, and are thus promising candidates in forthcoming applications of grammatical inference. In this paper, we pioneer the problem of their learnability. We propose a novel and sound algorithm (called LARS) which identifies a large subclass of them in polynomial time (but not data). We illustrate the execution of our algorithm through several examples, discuss the position of the class in the Chomsky hierarchy and finally raise some open questions and research directions. This work was supported in part by the IST Program of the European Community, under the PASCAL Network of Excellence, IST-2002-506778. This publication only reflects the authors’ views. Editor: Georgios Paliouras and Yasubumi Sakakibara     

Strong and NV-sequentiality of constructor systems

Constructor Systems (CSs) are an important subclass of Term Rewriting Systems (TRSs) which can be used as an abstract model of some programming languages. While normalizing strategies are always desirable for achieving a good computational behavior of programs, when dealing with lazy languages infinitary normalizing strategies should be considered instead since (finite approximations of ) infinite data structures can be returned as the result of computations. We have shown that NV-sequential TRSs (hence strongly sequential TRSs, a subclass of them) provide an appropriate basis for the effective definition of normalizing and infinitary normalizing strategies. In this paper, we show that strongly sequential and NV-sequential CSs coincide. Since the implementation of NV-sequential TRSs has been underexplored in comparison to strongly sequential TRSs, this coincidence suggests that, in programming languages, it is a good option to implement NV-sequentiality as strong sequentiality.     

DISTRIBUTED SIMULATION OF HIGH-LEVEL ALGEBRAIC PETRI NETS WITH LIMITED CAPACITY PLACES

The aim of this paper is to search for techniques to accelerate simulations exploiting the parallelism available in current multicomputers, and to use these techniques to study a class of Petri nets called high-level algebraic nets. These nets exploit the rich theory of algebraic specifications for high-level Petri nets. They also gain a great deal of modelling power by representing dynamically changing items as structured tokens whereas algebraic specifications turned out to be an adequate and flexible instrument for handling structured items. We focus on ECATNets (Extended Concurrent Algebraic Term Nets), a kind of high-level algebraic Petri nets with limited capacity places

Three distributed simulation techniques have been considered: asynchronous conservative, asynchronous optimistic and synchronous. These algorithms have been implemented in a network of workstations with MPI (Message Passing Interface). The influence that factors such as the characteristics of the simulated models, the organisation of the simulators and the characteristics of the target multicomputer have in the performance of the simulations have been measured and characterized

It is concluded that distributed simulation of ECATNets on a multicomputer system can in fact gain speedup over the sequential simulation, and this can be achieved even for small scale simulation models.     

Some Results on the Confluence Property of Combined Term Rewriting Systems

Generally speaking,confluence property is not preserved when Term Rewriting Systems (TRSs) are combined,even if they are canonical.In this paper we give some sufficient conditions for ensuring the confluence property of combined left-linear,overlapping TRSs.     

基于PI演算的反XML重写攻击安全模型验证

设计出一个安全模型后,要严格验证其是否满足安全需求是非常重要和必要的。利用形式化方法来检验模型是否满足了安全协议是一种有效的手段。本文针对XML重写攻击,设计出了一个反XML重写攻击的安全模型,然后运用Pi演算形式化方法验证了其有效性、真实性和安全性。     

项重写系统的并行实现方案

项重写系统的并行归约可以提高归约的效率，在无共享内存的Ｔｒａｎｓｐｕｔｅｒ网络上实现时要考虑任务的分配，项的拼装，归约任务的控制等问题，其中怎么样减少机间的机内进程的通信慢提高系统效果的关键。本文从控制方式角度讨论在不同拓扑结构的Ｔｒａｎｓｐｕｔｅｒ网络上实现项重写系统的方案，重点介绍基于树形结构下的控制方法，进程安排和通讯形式。     

Rational subsets of partially reversible monoids

A class of monoids that can model partial reversibility allowing simultaneously instances of two-sided reversibility, one-sided reversibility and no reversibility is considered. Some of the basic decidability problems involving their rational subsets, syntactic congruences and characterization of recognizability, are solved using purely automata-theoretic techniques, giving further insight into the structure of recognizable languages.     

Proving Modal Properties of Rewrite Theories Using Maude's Metalevel

Rewriting logic is a very expressive formalism for the specification of concurrent and distributed systems; more generally, it is a logic of change. In contrast, VLRL is a modal logic built on top of rewriting logic to reason precisely about that change. Here we present a technique to mechanically prove VLRL properties of rewrite theories using the reflective capability of rewriting logic through its Maude implementation.     

The rewriting logic semantics project

Rewriting logic is a flexible and expressive logical framework that unifies algebraic denotational semantics and structural operational semantics (SOS) in a novel way, avoiding their respective limitations and allowing succinct semantic definitions. The fact that a rewrite logic theory’s axioms include both equations and rewrite rules provides a useful “abstraction dial” to find the right balance between abstraction and computational observability in semantic definitions. Such semantic definitions are directly executable as interpreters in a rewriting logic language such as Maude, whose generic formal tools can be used to endow those interpreters with powerful program analysis capabilities.     

Actor languages their syntax, semantics, translation, and equivalence

In this paper we present two actor languages and a semantics preserving translation between them. The source of the translation is a high-level language that provides object-based programming abstractions. The target is a simple functional language extended with basic primitives for actor computation. The semantics preserved is the interaction semantics of actor systems — sets of possible interactions of a system with its environment. The proof itself is of interest since it demonstrates a methodology based on the actor theory framework for reasoning about correctness of transformations and translations of actor programs and languages and more generally of concurrent object languages.     

Infinitary rewriting: closure operators, equivalences and models

Infinitary Term Rewriting allows to express infinite terms and transfinite reductions that converge to those terms. Underpinning the machinery of infinitary rewriting are closure operators on relations that facilitate the formation of transfinite reductions and transfinite equivalence proofs. The literature on infinitary rewriting has largely neglected to single out such closure operators, leaving them implicit in definitions of (transfinite) rewrite reductions, or equivalence relations. This paper unpicks some of those definitions, extracting the underlying closure principles used, as well as constructing alternative operators that lead to alternative notions of reduction and equivalence. A consequence of this unpicking is an insight into the abstraction level at which these operators can be defined. Some of the material in this paper already appeared in Kahrs (2010). The paper also generalises the notion of equational model for infinitary rewriting. This leads to semantics-based notions of equivalence that tie in with the equivalences constructed from the closure operators.     

Reachability analysis of fragments of mobile ambients in AC term rewriting

In this paper, we investigate the connection between fragments of associative-commutative Term Rewriting and fragments of Mobile Ambients, a powerful model for mobile and distributed computations. The connection can be used to transfer decidability and undecidability results for important computational properties like reachability from one formalism to the other. Furthermore, it can be viewed as a vehicle to apply tools based on rewriting for the simulation and validation of specifications given in Mobile Ambients.     

不恢复余数阵列除法器的形式化描述和验证方法

本文使用重写技术对不恢复余数阵列除法器进行了形式化描述并结合归纳法对该除法器的正确性进行了验证,整个工作是建立在串行加法器的描述和验证基础上的。不恢复余数阵列除法器的运算和控制有一定的复杂度,适合用大规模集成电路实现。本文成功地用重写归纳法对它进行了描述和验证,说明重写归纳法在硬件电路正确性验证方面有广阔的应用前景。     

一种对MSR模型的新扩展

作为安全协议形式化建模方法之一的多集重写(MSR)模型虽然提供了基本的理论框架,但并不完善。针对其在类型攻击检测方面的不足,对原模型进行改进,扩展类型内容,丰富推演规则,使其能检测特定类型的攻击。给出安全属性的描述,并用实例验证扩展后的MSR模型中交换协议的非否认性和公平性。     

Using object-based analysis of image data to count birds: mapping of Lesser Flamingos at Kamfers Dam,Northern Cape,South Africa

Knowing instantaneous locations and numbers of individuals in animal populations is a major requirement for wildlife and conservation ecology. Recent advances in very high spatial resolution digital-imaging systems and in object-based image-analysis methods offer great potential for developing remote sensing in new application arenas, including direct mapping and counting of birds, mammals and other larger organisms. We present the successful application of an automated object-based image-mapping strategy that has been applied to total mapping, using aerial image data, of Phoeniconaias minor (Lesser Flamingo) individuals at Kamfers Dam, a large perennial lake in central South Africa. The object-based method used quadtree image segmentation and sequential object-brightness thresholding to identify individual birds with high accuracy (>99% compared to human visual interpretation). Accuracy-assessment results are presented, with discussion of the error factors related to the object-based method and the reference data. An under-estimation by the object-based method of less than 0.5% is indicated. The automated procedure mapped 81 664 Lesser Flamingos at this one site, which is 30% above the most recent estimated size of the entire southern Africa Lesser Flamingo population, indicating a need for further work to reassess this population's size.