On the refinement of liveness properties of distributed systems

We present a new approach, based on simulation relations, for reasoning about liveness properties of distributed systems. Our contribution consists of (1) a formalism for defining liveness properties, (2) a proof method for liveness properties based on that formalism, and (3) two expressive completeness results: our formalism can express any liveness property which satisfies a natural “robustness” condition; and also any liveness property at all, provided that history variables can be used. To define liveness, we generalize complemented-pairs (Streett) automata to an infinite state-space, and an infinite number of complemented-pairs. Our proof method provides two techniques: one for refining liveness properties across levels of abstraction, and another for refining liveness properties within a level of abstraction. The first is based on extending simulation relations so that they relate the liveness properties of an abstract automaton to those of a concrete automaton. The second is based on a deductive method for inferring new liveness properties of an automaton from already established liveness properties of the same automaton. This deductive method is diagrammatic, and is based on constructing “lattices” of liveness properties.     

Time-dependent distributed systems: proving safety,liveness and real-time properties

Most communication protocol systems utilize timers to implement real-time constraints between event occurrences. Such systems are said to betime-dependent if the real-time constraints are crucial to their correct operation. We present a model for specifying and verifying time-dependent distributed systems. We consider networks of processes that communicate with one another by message-passing. Each process has a set of state variables and a set of events. An event is described by a predicate that relates the values of the network's state variables immediately before to their values immediately after the event occurrence. The predicate embodies specifications of both the event's enabling condition and action. Inference rules for both safety and liveness properties are presented. Real-time progress properties can be verified as safety properties. We illustrate with three sliding window data transfer protocols that use modulo-2 sequence numbers. The first protocol operates over channels that only lose messages. It is a time-independent protocol. The second and third protocols operate over channels that lose, reorder, and duplicate messages. For their correct operation, it is necessary that messages in the channels have bounded lifetimes. They are time-dependent protocols.A. Udaya Shankar received the B. Tech. degree in Electrical Engineering from the Indian Institute of Technology, Kanpur, in 1976, the M.S. degree in Computer Engineering from Syracuse University, Syracuse, NY, in 1978, and the Ph.D. degree in Electrical Engineering from the University of Texas at Austin, in 1982. Since January 1983, he has been an Assistant Professor in the Department of Computer Science, University of Maryland, College Park. Since September 1985, he has been in the Institute for Advanced Computer Studies at the University of Maryland. His current research interests include modeling and verification of distributed systems, communication protocols, and real-time systems. He is a member of IEEE and ACM.Simon S. Lam is a Professor of Computer Sciences at the University of Texas at Austin and holds the Second David Bruton Jr. Centennial Professorship. His research interests are in the areas of computer networks, communication protocols, performance modeling, and the specification and verification of distributed systems. He serves on the editorial boards of three journals, IEEE Transactions on Communications, Performance Evaluation, and Proceedings of IEEE, and he is an IEEE Fellow. He received the BSEE degree (with Distinction) from Washington State University in 1969, and the MS and Ph.D. degrees from UCLA in 1970 and 1974 respectively. Prior to joining the University of Texas faculty, he was with the IBM T.J. Watson Research center from 1974 to 1977.Work supported by National Science Foundation under Grant No. ECS 85-02113Work supported by National Science Foundation under Grant No. ECS 83-04734     

大型复杂协议的形式化分析方法研究

大型复杂协议的形式化分析是目前研究的一个热点和难点.根据所采用技术的特点,将大型复杂协议的形式化分析方法分为基于逻辑推理的方法、基于模型检测的方法、基于定理证明的方法和基于进程代数的方法,并简要介绍了各类方法的代表性方法及验证器,最后对各类方法的特点进行分析和比较.指出迭式大型复杂协议的形式化分析方法未来的一个研究重点,修改原有方法或设计一种新的方法,使其既易自动化实现,又能用于复合协议的分析和验证.     

Detection of speaker liveness with CNN isolated word ASR for verification systems

Multimedia Tools and Applications - The article proposes a new speaker liveness test for speech verification systems. Biometric authentication systems based on speaker verification are often...     

Towards the construction of distributed detection programs,with an application to distributed termination

Summary Methodological design of distributed programs is necessary if one is to master the complexity of parallelism. The class of control programs, whose purpose is to observe or detect properties of an underlying program, plays an important role in distributed computing. The detection of a property generally rests upon consistent evaluations of a predicate; such a predicate can be global, i.e. involve states of several processes and channels of the observed program. Unfortunately, in a distributed system, the consistency of an evaluation cannot be trivially obtained. This is a central problem in distributed evaluations. This paper addresses the problem of distributed evaluation, used as a basic tool for solution of general distributed detection problems. A new evaluation paradigm is put forward, and a general distributed detection program is designed, introducing the iterative scheme ofguarded waves sequence. The case of distributed termination detection is then taken to illustrate the proposed methodological design. Jean-Michel Hélary is currently professor of Computer Science at the University of Rennes, France. He received a first Ph.D. degree in Numerical Analysis in 1968, then another Ph.D. Degree in Computer Science in 1988. His research interests include distributed algorithms and protocols, specially the methodological aspects. He is a member of an INRIA research group working at IRISA (Rennes) on distributed algorithms and applications. Professor Jean-Michel Hélary has published several papers on these subjects, and is co-author of a book with Michel Raynal. He serves as a PC member in an international conference. Michel Raynal is currently professor of Computer Science at the University of Rennes, France. He received the Ph.D. degree in 1981. His research interests include distributed algorithms, operating systems, protocols and parallelism. He is the head of an INRIA research group working at IRISA (Rennes) on distributed algorithms and applications. Professor Michel Raynal has organized several international conferences and has served as a PC member in many international workshops, conferences and symposia. Over the past 9 years, he has written 7 books that constitute an introduction to distributed algorithms and distributed systems (among them: Algorithms for Mutual Exclusion, the MIT Press, 1986, and Synchronization and Control of Distributed Programs, Wiley, 1990, co-authored with J.M. Hélary). He is currently involved in two european Esprit projects devoted to large scale distributed systems.This work was supported by French Research Program C³ on Parallelism and Distributed ComputingAn extended abstract has been presented to ISTCS '92 [12]     

Biotope: an integrated framework for simulating distributed multiagent computational systems

The study of distributed computational systems issues, such as heterogeneity, concurrency, control, and coordination, has yielded a number of models and architectures, which aspire to provide satisfying solutions to each of the above problems. One of the most intriguing and complex classes of distributed systems are computational ecosystems, which add an "ecological" perspective to these issues and introduce the characteristic of self-organization. Extending previous research work on self-organizing communities, we have developed Biotope, which is an agent simulation framework, where each one of its members is dynamic and self-maintaining. The system provides a highly configurable interface for modeling various environments as well as the "living" or computational entities that reside in them, while it introduces a series of tools for monitoring system evolution. Classifier systems and genetic algorithms have been employed for agent learning, while the dispersal distance theory has been adopted for agent replication. The framework has been used for the development of a characteristic demonstrator, where Biotope agents are engaged in well-known vital activities-nutrition, communication, growth, death-directed toward their own self-replication, just like in natural environments. This paper presents an analytical overview of the work conducted and concludes with a methodology for simulating distributed multiagent computational systems.     

An automated verification method for distributed systems softwarebased on model extraction

Software verification methods are used only sparingly in industrial software development today. The most successful methods are based on the use of model checking. There are, however, many hurdles to overcome before the use of model checking tools can truly become mainstream. To use a model checker, the user must first define a formal model of the application, and to do so requires specialized knowledge of both the application and of model checking techniques. For larger applications, the effort to manually construct a formal model can take a considerable investment of time and expertise, which can rarely be afforded. Worse, it is hard to secure that a manually constructed model can keep pace with the typical software application, as it evolves from the concept stage to the product stage. We describe a verification method that requires far less specialized knowledge in model construction. It allows us to extract models mechanically from source code. The model construction process now becomes easily repeatable, as the application itself continues to evolve. Once the model is constructed, existing model checking techniques allow us to perform all checks in a mechanical fashion, achieving nearly complete automation. The level of thoroughness that can be achieved with this new type of software testing is significantly greater than for conventional techniques. We report on the application of this method in the verification of the call processing software for a new telephone switch that was developed at Lucent Technologies     

Speculative locking protocols to improve performance for distributed database systems

We have proposed speculative locking (SL) protocols to improve the performance of distributed database systems (DDBSs) by trading extra processing resources. In SL, a transaction releases the lock on the data object whenever it produces corresponding after-image during its execution. By accessing both before and after-images, the waiting transaction carries out speculative executions and retains one execution based on the termination (commit or abort) mode of the preceding transactions. By carrying out multiple executions for a transaction, SL increases parallelism without violating serializability criteria. Under the naive version of SL, the number of speculative executions of the transaction explodes with data contention. By exploiting the fact that a submitted transaction is more likely to commit than abort, we propose the SL variants that process transactions efficiently by significantly reducing the number of speculative executions. The simulation results indicate that even with manageable extra resources, these variants significantly improve the performance over two-phase locking in the DDBS environments where transactions spend longer time for processing and transaction-aborts occur frequently.     

Variational embedding method and application to distributed systems control

The main aim of the present paper is to show the variational embedding method as a powerful tool for solving control problems associated with distributed systems. It is shown that, variational embedding subsumes many approximation methods that are available in the literature for solving constitutive equations of distributed systems. The well-known method of weighted residuals and its ramifications are shown to be the appropriate specializations of the embedding method. The method thus offers a vantage point from which it is conceptually easy to see both the plurality and unity of these methods. In the process of illustrating the hierarchy of the method, the attendant dilemma associated with the method of weighted residuals is successfully resolved. The variational embedding method yields a unified approach for obtaining lumped models for distributed parameter systems. The application is demonstrated by considering examples of engineering importance, and it is shown how lumped models of non-linear distributed systems could be constructed by methods other than the conventional discretization methods.     

Executable formal specifications of complex distributed systems with CoreASM

Formal specifications play a crucial role in the design of reliable complex software systems. Executable formal specifications allow the designer to attain early validation and verification of design using static analysis techniques and accurate simulation of the runtime behavior of the system-to-be. With increasing complexity of software-intensive computer-based systems and the challenges of validation and verification of abstract software models prior to coding, the need for interactive software tools supporting executable formal specifications is even more evident. In this paper, we discuss how CoreASM, an environment for writing and running executable specifications according to the ASM method, provides flexibility and manages the complexity by using an innovative extensible language architecture.     

Constructing formal rules to verify message communication in distributed systems

This study presents a method to construct formal rules used to run-time verify message passing between clients in distributed systems. Rules construction is achieved in four steps: (1) Visual specification of expected behavior of the sender, receiver, and network in sending and receiving a message, (2) Extraction of properties of sender, receiver, and network from the visual specification, (3) specification of constraints that should govern message passing in distributed systems, and (4) construction of verifier rules from the properties and the constraints. The rules are used to verify actual sender, receiver, and network behavior. Expected behavior of the client (process) is one that to be and the actual one is the behavior should be verified. The rules were applied to verify the behavior of client and servers that communicated with each other in order to compute Fibonacci numbers in parallel and some violations were discovered.     

Automatic verification for a class of distributed systems

Summary. The paper presents a new analysis method for a class of concurrent systems which are formed of several interacting components with the same structure. The model for these systems is composed of a control process and a set of homogeneous user processes. The control and user processes are modeled by finite labeled state transition systems which interact by means of enabling functions and triggering mechanisms. Based on this structure, an analysis method is presented which allows system properties, derived by reachability analysis for a finite number of user processes, to be generalized to an arbitrary number of user processes. A procedure for the automatic verification of properties such as mutual exclusion and absence of deadlocks is presented and is then used to provide for the first time a fully automated verification of the Lamport's fast mutual exclusion algorithm. Received: October 1998/Accepted January 2000     

Efficient verification of distributed real-time systems with broadcasting behaviors

Binary synchronization has been used extensively in the construction of mathematical models for the verification of embedded systems. Although it allows for the modeling of complex cooperation among many processes in a natural environment, not many tools have been developed to support the modeling capability in this regard. In this article, we first give examples to argue that special algorithms are needed for the efficient verification of systems with complex synchronizations. We then define our models of distributed real-time systems with synchronized cooperation among many processes. We present algorithms for the construction of BDD-like diagrams for the characterization of complex synchronizations among many processes. We present weakest precondition algorithms that take advantage of the just-mentioned BDD-like diagrams for the efficient verification of complex real-time systems. Finally, we report experiments and argue that the techniques could be useful in practice.     

Architecturing large integrated complex information systems: an application to healthcare

The global enterprise-wide approaches help organizations to model and understand the enterprise key components and their relationships and manage the organizations’ transformations and change. However, many of these approaches lack of insights into how to manage complexities related to the multitude of applications developed in silos such as the various systems in health organizations that were designed independently from each other. This paper contributes to the solutions addressing this issue by proposing a methodology and tools to create foundations based on key components to help develop the information architecture at the heart of the enterprise architecture that can guarantee the evolution of the organization. These core components are a set of reusable Field Actions representing the non-contextual persistent information, a common canonical Corporate Conceptual Data Model capturing all the vital data in the organization, and Views or sub-schema of this global data model that represent information for different stakeholders in the organization. To show the effectiveness of the proposed approach and to gain more insights into its practical value, the architecturing approach is applied in the healthcare domain to create the information architecture and the enterprise architecture for the Quebec healthcare network.     

Broadcast psi-calculi with an application to wireless protocols

Psi-calculi is a parametric framework for the extensions of pi-calculus, with arbitrary data structures and logical assertions for facts about data. In this paper we add primitives for broadcast communication in order to model wireless protocols. The additions preserve the purity of the psi-calculi semantics, and we formally prove the standard congruence and structural properties of bisimilarity. We demonstrate the expressive power of broadcast psi-calculi by modelling the wireless ad hoc routing protocol LUNAR and verifying a basic reachability property.     

Mission reliability of an automatic control system integrated with distributed intelligent built-in-test systems

This paper introduces distributed-centralized Built-in-Test (BIT) systems interfaced with an automatic control system with the purpose of improving mission reliability. By Using a block diagramming method, a complicated system is decomposed into mutually exclusive subsystems so that a distributed BIT is connected to each subsystem for multiple parallel processing of fault direction. The data produced by the distributed BITs is sent to a central control processor. We present a Markov process approach to analytically derive the mission reliability of an automatic control fault-tolerant system with distributed BITs. As diagnostic mistakes of the BIT, the false alarm and fault missing of BIT are considered with the malfunction of the BIT itself. Numerical examples are also prepared to evaluate the performance of distributed intelligent BITs, by comparing mission reliabilities corresponding to the variation of design parameters in a time domain.     

Automatic verification of distributed systems: The process algebra approach

A survey of tools for the analysis of distributed systems represented through process algebras is presented. The tools are compared with respect to a set of qualitative parameters. From this analysis, the properties which are desirable for concurrency tools are investigated. Criteria to evaluate the suitability of a tool with respect to a particular user are proposed.     

Development of formal models and conformance testing for systems with asynchronous interfaces and telecommunications protocols

There is a gap between the formal modeling and testing methods for modern protocols and asynchronous software systems: due to high complexity of such systems, attempts to include formal models in testing procedures fail. In this paper, we propose an approach to filling this gap based on a formalization of the behavior of systems with asynchronous interfaces using contract specifications followed by the use of these specifications to design adaptive test suites. This approach was used for testing various software systems including implementations of the IPv6 Internet protocols stack and implementations of the POSIX and Linux Standard Base software interfaces.