并发模型的分类与层次

随着处理器性能的不断提高和网络技术的迅速发展,越来越多的计算机应用系统涉及并行与分布式计算。开发这类系统远比传统的串行系统困难,这除了并行与分布式计算本身固有的复杂性外,还有一个原因是人们对并发性的实质缺乏真正了解,因而对并发模型进行深入广泛的研究具有重要的现实意义。并发模型是一种描述与解释并发与分布式系统的形式化数学模型,在理论上可提供对并发系统及其行为的深刻理解,在实践中可为并发系统的设计与分析提供指导方法。探讨并发性的语义往往也集中在并发模型的研究,以此作为并发语言与系统的指称结构。     

LASS: A language for stochastic systems

A new problem oriented language for finding solutions to problems to probability theory is presented. A system is first described as a structure of probabilistic cause and effect relationships. The, questions concerning outcome probabilities are posed. The programming system then provides exact answers to such questions by applying discrete probability theory.     

Expansion Nets and Expansion Processes of Elementary Net Systems

Occurrence nets are insufficient to precisely describe executions of elementary net systems with contacts.Traditionally,S-complementation is used for removal of contacts from the systems.Although the main behavior and properties of the original elementary net systems are preserved during S-complementation,their topologies may be changed greatly.This paper introduces a new kind of nets-expansion nets-for representing behavior of elementary net systems.As shown in the paper,expansion nets are natural as well as sufficient for describing the precise behavior of elementary net systems with or without contactks.     

On location observability notions for switching systems

The focus of this paper is on the analysis of initial discrete state distinguishability notions for switching systems, in a discrete time setting. Moreover, the relationship between initial discrete state distinguishability and the problem of reconstructing the current discrete state is addressed.     

Knowledge-based systems in context: A methodological approach to the qualitative issues

Knowledge-Based Systems (KBS) are developed to contain substantial elements of human knowledge and expertise in a well-defined domain, and use these to support user or expert tasks. Issues related to the social and organisational contexts of these systems are widely acknowledged to be particularly critical to their success. However, methodology proposals usually stop short of adequately handling soft and unstructured data that frame the contexts of use. The handling of qualitative data needs to be done in a way that directly impinges on the wider Knowledge-Based System engineering processes and decisions. In this paper, we discuss the nature of context-sensitive issues, and describe a methodological approach for resolving them through the rigorous analysis of qualitative data, using a methodology which is based upon the Grounded Theory method from the social sciences.     

Mutually nonblocking supervisory control of discrete event systems

A single maximally permissive and nonblocking supervisor to simultaneously fulfill several marked specifications pertaining to a single plant is investigated. Given a plant G and two marked specification languages K₁ and K₂, a supervisor S is said to be (K₁,K₂)-mutually nonblocking if (for i,j=1,2)

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. This means that when the closed-loop system marks a trace of K_i, then it is always able to continue to a trace of K_j, also marked in the closed-loop system. Thus, the controlled system can execute traces within one specification while always being able to continue a trace of the other and hence not blocking the other specification. A complete, globally nonblocking and (K₁,K₂)-mutually nonblocking supervisor such that L_m(G || S)K₁K₂ exists if and only if there exists a controllable mutually nonblocking sublanguage of the union of the specifications. There does exist a supremal such language. Furthermore, in the case that each specification is nonconflicting with respect to the prefix-closure of the other, this supremal language can be calculated by expressing it as the union of the supremal prefix-bounded sublanguages of the respective specifications. Finally, we show that the multiply nonblocking supervision of Thistle, Malhame, Hoang and Lafortune ((1997). Internal Report, Dept. de genie electrique et de genie informatique, Ecole Polytechnique de Montreal, Canada) is equivalent to globally and mutually nonblocking supervision.     

EQL: A language for numerical computation

EQL, a language for numerical computation, has been implemented. This paper describes essential properties of the EQL language, which considerably simplifies numerical analysis and programming thanks to the following features: (1) elimination of explicit sequencing: (2) matrix and array computations: (3) simple and convenient notation of iteration procedure: (4) mapping of data structures (vector or matrix) on data objects which are represented in the computer: (5) tabulation facility for function values. Also the outline of translator, which transforms an EQL program to FORTRAN codes, is described.     

Developing multiagent systems for design activity analysis

Engineering design is a complex socio-technical activity characterized by co-evolution of problem and solution. However, the actual design theories are not well-suited to represent and model the complexity of design activity, the co-evolution and its dynamics. Therefore, there is a need to develop design activity reasoning theories and tools, which can theorize and simulate the model of co-evolution and its dynamics. Multiagent systems have the capacity to play an important role in developing and analyzing models and theories of interactivity in socio-technical societies, particularly in design. This paper first addresses a theory for design activity reasoning. Then, it will present a multiagent system, called ADEA (Agents-based DEsign activity Analysis), in order to model, simulate and analyze this theory. The agents of the ADEA platform formalize the necessary design roles, characterizing the design activity as well as the relationship between design parameters in the design space. ADEA’s platform shows that cognitive limitation of role agents has been overcome, considering their relationship with the design space modeled as a network of design parameter agents.     

A visual language‐based system for extraction–transformation–loading development

Data warehouse loading and refreshment is typically performed by means of complex software processes called extraction–transformation–loading (ETL). In this paper, we propose a system based on a suite of visual languages for mastering several aspects of the ETL development process, turning it into a visual programming task. The approach can be easily generalized and applied to other data integration contexts beyond data warehouses. It introduces two new visual languages that are used to specify the ETL process, which can also be represented by means of UML activity diagrams. In particular, the first visual language supports data manipulation activities, whereas the second one provides traceability information of attributes to highlight the impact of potential transformations on integrated schemas depending on them. Once the whole ETL process has been visually specified, the designer might invoke the automatic generation of an activity diagram representing a possible orchestration of it based on its dependencies. The designer can edit such a diagram to modify the proposed orchestration provided that changes do not alter data dependencies. The final specification can be translated into code that is executable on the data sources. Finally, the effectiveness of the proposed approach has been validated through a user study in which we have compared the effort needed to design an ETL process in our approach with respect to the one required with main visual approaches described in the literature.Copyright © 2013 John Wiley & Sons, Ltd.     

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     

A characterization of (regular) circular languages generated by monotone complete splicing systems

Circular splicing systems are a formal model of a generative mechanism of circular words, inspired by a recombinant behaviour of circular DNA. Some unanswered questions are related to the computational power of such systems, and finding a characterization of the class of circular languages generated by circular splicing systems is still an open problem. In this paper we solve this problem for monotone complete systems, which are finite circular splicing systems with rules of a simpler form. We show that a circular language L is generated by a monotone complete system if and only if the set Lin(L) of all words corresponding to L is a pure unitary language generated by a set closed under the conjugacy relation. The class of pure unitary languages was introduced by A. Ehrenfeucht, D. Haussler, G. Rozenberg in 1983, as a subclass of the class of context-free languages, together with a characterization of regular pure unitary languages by means of a decidable property. As a direct consequence, we characterize (regular) circular languages generated by monotone complete systems. We can also decide whether the language generated by a monotone complete system is regular. Finally, we point out that monotone complete systems have the same computational power as finite simple systems, an easy type of circular splicing system defined in the literature from the very beginning, when only one rule of a specific type is allowed. From our results on monotone complete systems, it follows that finite simple systems generate a class of languages containing non-regular languages, showing the incorrectness of a longstanding result on simple systems.     

Computers and writing: Casting a broader net with theory and research

Today, teachers of English are faced with the problem of developing new vantage points from which to consider the use of computers in writing programs, writing classrooms, and individual writing processes. Until this time, the profession has subscribed to a limited view of computers and their effects on writing — a view circumscribed by the paradigms of other disciplines or by our own past experiences with teaching machines and paper-and-pencil composing. These visions are not capable of accommodating the larger and more radical changes wrought by the electronic medium we are now using. By subscribing to them, English teachers may, as Coleridge says, have created a tacit compact not to pass beyond a certain limit in speculating about computers. This paper suggests four overlapping areas of exploration, four points of departure that might help us spark creative re-formations of our thinking about computers and their relationship to writing: 1.) Computers and teaching writing, 2.) Computers and language theory, 3.) Computers and learning from the past, 4.) Computer research in other fields.Cynthia Selfe has been chair of the NCTE assembly of Computers in English and a member of the CCCC Committee on Instructional Technology. Billie J. Wahlstrom is chair of the Graduate Program in Rhetoric and Technical Communication at Michigan Technological University and a consultant on interactive videodisc design for Michigan Tech Software.     

The context-splittable normal form for Church–Rosser language systems

In this paper the context-splittable normal form for rewriting systems defining Church–Rosser languages is introduced. Context-splittable rewriting rules look like rules of context-sensitive grammars with swapped sides. To be more precise, they have the form uvw→uxw with u,v,w being words, v being nonempty and x being a single letter or the empty word. It is proved that this normal form can be achieved for each Church–Rosser language and that the construction is effective. Some interesting consequences of this characterization are given, too.     

Near net shape technology: An innovative opportunity for the automotive industry

Near net shape is an innovative concept in industrial manufacturing. The main focus of this technology is to produce parts, as near as possible close to their final shape and contour, implementing non-chipping techniques. In this way the manufacturing gives the possibility of a finished product with minimal cutting. Near net shape technology also generates the opportunity to reduce the productive steps for a given process chain. Both the above-mentioned characteristics have the same main goal: achieving cost reduction. This fundamental target incorporates several other advantages, such as: reduction of process variability, quality improvement in the finished product and the possibility to focus the design of mechanical devices on functional features, eliminating technical constraints imposed by the process. Based on these factors and in cooperation with the IWU Fraunhofer Institut of Chemnitz, the authors conducted a research regarding the manufacturing of an innovative automotive gear shaft, produced by applying near net shape processes. The goal of this study is to evaluate whether it is more convenient to produce the part implementing a traditional production chain or an innovative one, based on near net shape techniques. The first step was to locate the available technologies in order to produce the selected part. There are two alternatives: a traditional cutting manufacture, performed with a numerical control turning machine and a near-net-shape technique, characterized only by deformation processes. The next step was to detect the main differential costs between the two opportunities. Comparing technical data and information available in literature, the authors detected the main differential voices of cost: raw material, amortization, manpower and direct setup. In order to make the study more reliable, the authors assumed an actual industrial environment, featured by an annual demand of 400,000 pieces and a product lifetime cycle of 10 yr. The evaluation led to the conclusion that the innovative manufacturing chain is more convenient.     

Decision procedures for elementary sublanguages of set theory

In this paper we prove the decidability of the class of unquantified formulae of set theory involving the operators , , , \, {·}, pred _< and the predicates =, , , Finite, where pred _<(s) denotes the collection of all sets having rank strictly less than the rank of s.This work generalizes and combines earlier results published in the same series of papers.This work has been partially supported by ENI and ENIDATA within the AXL project.     

An operator net model for distributed systems

An operator net is a graph consisting of nodes and directed arcs. While operator nets are syntactically similar to dataflow nets, they completely separate the operational semantics from the mathematical semantics. In this paper we define an operational semantics for operator nets that intuitively corresponds to communication in a distributed system. The operational semantics of operator ator nets provide a formal model for a distributed system that is an intermediate point between the actual system and a mathematical model. Abstract properties are expressed using relations on events and messages of an operator net. Corresponding operational specifications can be written using Lucid equations that define a node as a mathematical function on infinite history sequences. The operational specifications are executable and can be easily transformed into a practical implementation of the system. Examples of such specifications are included in the paper.Janice Glasgow is an associate professor in the Department of Computing and Information Science at Queen's University. She received her M. Math and Ph.D. degrees from the University of Waterloo. Dr. Glasgow's current research interests include programming language semantics and logics for reasoning about programming.Glenn H. MacEwen r received the B.Eng. degree in electrical engineering from McGill University, Montreal, P.Q., Canada, in 1962 and the M.Sc. and Ph.D. degrees in computer science from the University of Toronto, Toronto, Ont., Canada in 1967 and 1971, respectively. Since 1970 he has been with the Department of Computing and Information Science at Queen's University, Kingston, Ontario. He served as Head from 1982 to 1987 and is currently a Professor in the department. He is also a director and consultant to Andyne Computing Limited. His research interests include software engineering, computer security, and real-time systems. Dr. MacEwen is a senior member of the Institute of Electrical and Electronics Engineers, and a member of the Association for Computing Machinery and the Association of Professional Engineers of Ontario.     

Multi-objective reliability optimization for dissimilar-unit cold-standby systems using a genetic algorithm

A genetic algorithm approach is used to solve a multi-objective discrete reliability optimization problem in a k dissimilar-unit non-repairable cold-standby redundant system. Each unit is composed of a number of independent components with generalized Erlang distributions arranged in a series–parallel configuration. There are multiple component choices with different distribution parameters available for being replaced with each component of the system. The objective of the reliability optimization problem is to select the best components, from the set of available components, to be placed in the standby system in order to minimize the initial purchase cost of the system, maximize the system MTTF (mean time to failure), minimize the system VTTF (variance of time to failure) and also maximize the system reliability at the mission time. Finally, we apply a genetic algorithm with double strings using continuous relaxation based on reference solution updating (GADSCRRSU) to solve this multi-objective problem, using goal attainment formulation. The results are also compared against the results of a discrete-time approximation technique to show the efficiency of the proposed GA approach.