Petri net based Grid workflow verification and optimization

Graphical workflow modeling tools, such as UML and DAG, can facilitate users to express workflow process logic, but lack of abilities to carry out simulation and correctness checking. In this paper, based on Petri net, we propose a service composition oriented Grid workflow model and its related six elementary workflow patterns: sequence, condition, iteration, concurrency, synchronization, and triggering. In addition, we present our Grid workflow analysis approaches on three aspects: workflow reachability verification, workflow deadlock verification, and workflow optimization. The experimental results show that our workflow verification and optimization mechanisms are feasible and efficient.     

Formalizing the specification and execution of workflows using the event calculus

The event calculus is a logic programming formalism for representing events and their effects especially in database applications. This paper proposes the event calculus as a logic-based methodology for the specification and execution of workflows. It is shown that the control flow graph of a workflow specification can be expressed as a set of logical formulas and the event calculus can be used to specify the role of a workflow manager through a set of rules for the execution dependencies of activities. The proposed framework for a workflow manager maintains a history of events to control the execution of activities. The events are instructions to the workflow manager to coordinate the execution of activities. Based on the already occurred events, the workflow manager triggers new events to schedule new activities in accordance with the control flow graph of the workflow. The net effect is an alternative approach for defining a workflow engine whose operational semantics is naturally integrated with the operational semantics of a deductive database. Within this framework it is possible to model sequential and concurrent activities with or without synchronization. It is also possible to model agent assignment and execution of concurrent workflow instances. The paper, thus, contributes a logical perspective to the task of developing formalization for the workflow management systems.     

Logic-based 2D geometric modeling in a CAD environment

This paper examines the use of predicate logic for deductive construction of geometric models. The process of logical inference and its use for geometric modeling is examined. The logic-based definition of a retaining wall is presented, the implementation of a logic-based CAD system using a commercial software is briefly discussed and its use is illustrated.     

A practical method to analyze workflow logic models

The analysis of workflow is crucial to the correctness of workflow applications. This paper introduces a simple and practical method for analyzing workflow logic models. Firstly, some definitions of the models and some properties, such as throughness, no‐redundant‐transition and boundedness, are presented. Then, we propose an approach based on synchronized reachability graphs (SRGs) to verify these properties. The SRG uses the characteristics of synchronizers in workflow logic models and mitigates the state explosion by constructing synchronized occurrence sequences rather than interleaving occurrence sequences. This paper also proposes some refined and feasible reduction rules which can preserve vital properties of workflow logic models. Using these two techniques, the SRG‐based verification method can achieve higher efficiency. Furthermore, this research also develops a verification tool based on the method, presents the analysis results of some practical cases and compares our method with others. Copyright © 2007 John Wiley & Sons, Ltd.     

Modeling and formal verification of embedded systems based on a Petri net representation

In this paper we concentrate on aspects related to modeling and formal verification of embedded systems. First, we define a formal model of computation for embedded systems based on Petri nets that can capture important features of such systems and allows their representation at different levels of granularity. Our modeling formalism has a well-defined semantics so that it supports a precise representation of the system, the use of formal methods to verify its correctness, and the automation of different tasks along the design process. Second, we propose an approach to the problem of formal verification of embedded systems represented in our modeling formalism. We make use of model checking to prove whether certain properties, expressed as temporal logic formulas, hold with respect to the system model. We introduce a systematic procedure to translate our model into timed automata so that it is possible to use available model checking tools. We propose two strategies for improving the verification efficiency, the first by applying correctness-preserving transformations and the second by exploring the degree of parallelism characteristic to the system. Some examples, including a realistic industrial case, demonstrate the efficiency of our approach on practical applications.     

Proving Consistency Assertions for Automotive Product Data Management

We present a formal specification and verification approach for industrial product data bases containing Boolean logic formulae to express constraints. Within this framework, global consistency assertions about the product data are converted into propositional satisfiability problems. Today"s state-of-the-art provers turn out to be surprisingly efficient in solving the SAT-instances generated by this process. Moreover, we introduce a method for encoding special nonmonotonic constructs in traditional Boolean logic. We have successfully applied our method to industrial automotive product data management and could establish a set of commercially used interactive tools that facilitate the management of change and help raise quality standards.     

基于UML-Statecharts的工作流控制结构的验证

工作流模型验证成为工作流的重要研究领域之一。控制结构的正确性是工作流过程所需达到的最基本要求,本文着重控制结构方面的验证。本文使用UML-Statecharts建立控制结构模型,使用时序逻辑表示工作流控制结构需要满足的性质。给出了一个定理并进行了证明,基于定理给出了一个验证完全性的算法,对于工作流语义相关性质的验证给出了一模型检测算法。     

Expressive Completeness of Duration Calculus

This paper compares the expressive power of first-order monadic logic of order, a fundamental formalism in mathematical logic and the theory of computation, with that of the propositional version of duration calculus (PDC), a formalism for the specification of real-time systems. Our results show that the propositional duration calculus is expressively complete for first-order monadic logic of order. Our semantics for PDC conservatively extends the standard semantics to all positive (including infinite) length intervals. Hence, in view of the expressive completeness, liveness properties can be specified in PDC. This observation refutes a widely believed misconception that the duration calculus cannot specify liveness properties.     

Encoding deductive argumentation in quantified Boolean formulae

There are a number of frameworks for modelling argumentation in logic. They incorporate a formal representation of individual arguments and techniques for comparing conflicting arguments. A common assumption for logic-based argumentation is that an argument is a pair 〈Φ,α〉 where Φ is minimal subset of the knowledge-base such that Φ is consistent and Φ entails the claim α. Different logics provide different definitions for consistency and entailment and hence give us different options for argumentation. Classical propositional logic is an appealing option for argumentation but the computational viability of generating an argument is an issue. To better explore this issue, we use quantified Boolean formulae to characterise an approach to argumentation based on classical logic.     

The INFOLOG linear tense propositional logic of events and transactions

An extended linear tense propositional logic is presented for the specification and verification of the behavior of very dynamic information systems. The temporal evolution of a system is described with causal rules specifying trigger/reaction relationships between events. Besides the presentation of the language, semantics and axiomatization of the proposed triggering logic, a practical proof system is outlined which provides effective tools for proving both safety and liveness properties of the specified systems. Its usefulness is illustrated by proving several properties of a system using semaphores. The relationship between the event structure and the tense structure of the logic is also discussed. The proposed logic is an important fragment of the INFOLOG calculus that is being developed for information systems design.     

Propositional Logic Constraint Patterns and Their Use in UML-Based Conceptual Modeling and Analysis

An important conceptual modeling activity in the development of database, object-oriented and agent-oriented systems is the capture and expression of domain constraints governing underlying data and object states. UML is increasingly used for capturing conceptual models, as it supports conceptual modeling of arbitrary domains, and has extensible notation allowing capture of invariant constraints both in the class diagram notation and in the separately denoted OCL syntax. However, a need exists for increased formalism in constraint capture that does not sacrifice ease of use for the analyst. In this paper, we codify a set of invariant patterns formalized for capturing a rich category of propositional constraints on class diagrams. We use tools of Boolean logic to set out the distinction between these patterns, applying them in modeling by way of example. We use graph notation to systematically uncover constraints hidden in the diagrams. We present data collected from applications across different domains, supporting the importance of "pattern-finding" for n-variable propositional constraints using general graph theoretic methods. This approach enriches UML-based conceptual modeling for greater completeness, consistency, and correctness by formalizing the syntax and semantics of these constraint patterns, which has not been done in a comprehensive manner before now     

Extended IF逻辑的命题演算系统

Extended IF 逻辑是一阶逻辑的扩张,其主要特点是可表达量词间的相互依赖和独立关系,但其命题部分至今没有得到公理化.基于Cirquent 演算方法,给出了一个关于Cirquent 语义(命题水平)可靠完备的形式系统.该系统能够很好地解释和表达命题联结词间的相互依赖和独立关系,从而使Extended IF 逻辑在命题水平得到了真正意义上的公理化.     

Probabilistic rule-based argumentation for norm-governed learning agents

This paper proposes an approach to investigate norm-governed learning agents which combines a logic-based formalism with an equation-based counterpart. This dual formalism enables us to describe the reasoning of such agents and their interactions using argumentation, and, at the same time, to capture systemic features using equations. The approach is applied to norm emergence and internalisation in systems of learning agents. The logical formalism is rooted into a probabilistic defeasible logic instantiating Dung??s argumentation framework. Rules of this logic are attached with probabilities to describe the agents?? minds and behaviours as well as uncertain environments. Then, the equation-based model for reinforcement learning, defined over this probability distribution, allows agents to adapt to their environment and self-organise.     

在NiosⅡ系统设计中SignalTabⅡ的应用

通过对Altera公司的SignalTap Ⅱ基于逻辑分析核的嵌入式逻辑分析仪的特点及使用方法的介绍,并结合实例说明SignalTap Ⅱ为SOPC设计,提供了实时可视性,减少了验证过程的时间,     

Hierarchical multi-layer CAD system for systematic design of complex logic controllers

Logic controllers play an extremely important role in the control of both continuous-time and discrete-time systems. However, the design process of logic controllers is not supported yet by a structured and integrated set of CAD/CAE tools for their specification, validation and interaction with the process. In addition, there is no consolidated standard in the international community. In this paper, a formalism is proposed, based on Petri nets, implementing a hierarchical/modular representation of logic controllers, suitable for the systematic development of complex programs; moreover, a theoretical and practical framework is established to formally verify the basic properties that a logic controller must possess. The developments illustrated here are especially effective in the perspective of design. The realization of a prototype CAD/CAE environment to design logic controllers is also described. Finally, an application example is developed and discussed.     

On design,verification, and dynamic modification of the problem-based scientific workflow model

A science process is a process to solve complex scientific problems which usually have no mature solving methods. Science processes if modeled in workflow forms, i.e. scientific workflows, can be managed more effectively and performed more automatically. However, most current workflow models seldom take account of specific characteristics of science processes and are not very suitable for modeling scientific workflows. Therefore, a new workflow model named problem-based scientific workflow model (PBSWM) is proposed in this paper to accommodate those specific characteristics. Corresponding soundness verification and dynamic modification are discussed accordingly based on the new modelling method. This paper makes three main contributions: (1) three new constructs are proposed for special logic semantics in science processes; (2) verification is deployed with the consideration from both data-specific perspective and control-specific perspective; and (3) a set of rules are provided to automatically infer passive modifications caused by other modifications.