Reduction rules for reset/inhibitor nets

Reset/inhibitor nets are Petri nets extended with reset arcs and inhibitor arcs. These extensions can be used to model cancellation and blocking. A reset arc allows a transition to remove all tokens from a certain place when the transition fires. An inhibitor arc can stop a transition from being enabled if the place contains one or more tokens. While reset/inhibitor nets increase the expressive power of Petri nets, they also result in increased complexity of analysis techniques. One way of speeding up Petri net analysis is to apply reduction rules. Unfortunately, many of the rules defined for classical Petri nets do not hold in the presence of reset and/or inhibitor arcs. Moreover, new rules can be added. This is the first paper systematically presenting a comprehensive set of reduction rules for reset/inhibitor nets. These rules are liveness and boundedness preserving and are able to dramatically reduce models and their state spaces. It can be observed that most of the modeling languages used in practice have features related to cancellation and blocking. Therefore, this work is highly relevant for all kinds of application areas where analysis is currently intractable.     

Petri net-based process monitoring: a workflow management system for process modelling and monitoring

Nowadays business process management is becoming a fundamental piece of many industrial processes. To manage the evolution and interactions between the business actions it is important to accurately model the steps to follow and the resources needed by a process. Workflows provide a way of describing the order of execution and the dependencies between the constituting activities of business processes. Workflow monitoring can help to improve and avoid delays in industrial environments where concurrent processes are carried out. In this article a new Petri net extension for modelling workflow activities together with their required resources is presented: resource-aware Petri nets (RAPN). An intelligent workflow management system for process monitoring and delay prediction is also introduced. Resource aware-Petri nets include time and resources within the classical Petri net workflow representation, facilitating the task of modelling and monitoring workflows. The workflow management system monitors the execution of workflows and detects possible delays using RAPN. In order to test this new approach, different services from a medical maintenance environment have been modelled and simulated.     

基于Petri网化简技术的工作流模型正确性研究

为了更有效地对工作流模型进行分析验证，提出了一种基于Petri网化简技术的工作流模型正确性验证方法。在对各种工作流模型验证技术深入研究的基础上，通过对非自由选择网结构活性和有界性的分析，给出了针对Petri网中非自由选择部分的分析方法。在保持活性和有界性的前提下，给出了将活的且有界的非自由选择部分转化为自由选择部分的转化方法，从而将非自由选择的Petri网验证问题转化为自由选择Petri网的验证问题。通过一个例子说明了如何使用该文提出的方法来验证模型的正确性。     

Reduction rules for YAWL workflows with cancellation regions and OR-joins

As the need for concepts such as cancellation and OR-joins occurs naturally in business scenarios, comprehensive support in a workflow language is desirable. However, there is a clear trade-off between the expressive power of a language (i.e., introducing complex constructs such as cancellation and OR-joins) and ease of verification. When a workflow contains a large number of tasks and involves complex control flow dependencies, verification can take too much time or it may even be impossible. There are a number of different approaches to deal with this complexity. Reducing the size of the workflow, while preserving its essential properties with respect to a particular analysis problem, is one such approach. In this paper, we present a set of reduction rules for workflows with cancellation regions and OR-joins and demonstrate how they can be used to improve the efficiency of verification. Our results are presented in the context of the YAWL workflow language.     

延迟时间Petri网的验证分析

延迟时间Petri网（Delay Time Petri Nets，DTPN）是一类重要的时间扩展Petri网系统，解决了其他时间扩展Petri网（如时间Petri网）在保存时间约束时所面临的困难。可调度验证的目的是验证工作流模型时间约束的合理性，对流程实例的时间可达性进行仿真。提出一种基于DTPN的时间约束工作流验证分析方法。给出了DTPN的相关定义，并结合工作流控制结构描述了变迁可触发的时间条件；提出了DTPN触发点的概念以及基于此的验证分析算法；简要分析了DTPN的特性。DTPN的研究丰富完善了现有时间Petri网体系，具有积极的意义。     

Development of context-aware workflow systems based on Petri Net Markup Language

The Petri Net Markup Language (PNML) is originally an XML-based interchange format for Petri nets. Individual companies may specify their process models in Petri nets and exchange the Petri nets with other companies in PNML. This paper aims to demonstrate the capabilities of PNML in the development of applications instead of an industrial interchange format only. In this paper, we apply PNML to develop context-aware workflow systems. In existing literature, different methodologies for the design of context-aware systems have been proposed. However, workflow models have not been considered in these methodologies. Our interests in this paper are to propose a methodology to automatically generate context-aware action lists for users and effectively control resource allocation based on the state of the workflow systems. To achieve these objectives, we first propose Petri net models to describe the workflows. Next, we propose models to capture resource activities. Finally, the interactions between workflows and resources are combined to obtain a model for the whole processes. Based on the combined model, we propose architecture to automatically generate context-aware graphical user interface to guide the users and control resource allocation in workflow systems. We demonstrate our design methodology using a health care example.     

基于反应型的Petri网工作流业务过程建模

传统的基于令牌机制的Petri网工作流模型虽然被广泛应用,但不能完整准确地反映工作流引擎运行时的实际情况。在充分考虑了系统运行时的实际场景之后,提出了一种基于反应型机制的Petri网工作流模型;然后分析了标准Petri网工作流模型到反应型Petri网工作流模型的转换方法和实现步骤,并给出了验证的思路。     

基于Petri网的复合Web Service构造与分析

利用Petri网对工作流模型进行分析与验证是目前行之有效的一种方法。该文应用工作流思想研究Web Services的复合问题,利用Petri网技术分析Web Services的调用过程,并对Web Services网进行形式化分析,给出Web Services复合群到工作流网的映射规则。     

基于工作流网的实时协同系统模拟技术

基于Petri网和工作流的概念，提出一种实时协同系统的形式化模拟与分析技术——逻辑工作流网，逻辑工作流网是抑制弧Petri网和高级Petri网的抽象和扩展，其变迁的输入／输出受逻辑表达式的约束，它与一般工作流网相比，能够在一定程度上缓解状态空间爆炸问题，且便于系统设计人员掌握和使用，该文分析了逻辑工作流网的若干性质及组合网的性质继承问题，并以网上企业销售系统为例，说明逻辑工作流网在实时协同系统模拟分析中的应用。     

Verifying soundness of business processes: A decision process Petri nets approach

This paper presents a trajectory-tracking approach for verifying soundness of workflow/Petri nets represented by a decision-process Petri net. Well-formed business processes correspond to sound workflow nets. The advantage of this approach is its ability to represent the dynamic behavior of the business process. We show that the problem of finding an optimum trajectory for validation of well-formed business processes is solvable. To prove our statement we use the Lyapunov stability theory to tackle the soundness verification problem for decision-process Petri nets. As a result, applying Lyapunov theory, the well-formed verification (soundness) property is solved showing that the workflow net representation using decision process Petri nets is uniformly practically stable. It is important to note that in a complexity-theoretic sense checking the soundness property is computationally tractable, we calculate the computational complexity for solving the problem. We show the connection between workflow nets and partially ordered decision-process Petri net used for business process representation and analysis. Our computational experiment of supply chains demonstrate the viability of the modeling and solution approaches for solving computer science problems.     

基于时间约束Petri网的工作流可调度性分析

引入时间参数控制工作流高效执行是工作流技术研究的重要内容之一。在工作流的Petri网模型中引入时间参数,不仅可以对工作流中的活动进行时间约束,而且能建立相应的工作流时间约束Petri网模型。文中在分析该模型的时间约束和可调度性的基础上,提出了对工作流可调度性分析验证方法及其相应的算法,最后通过一个实例说明了分析验证的过程。     

Modeling and Analysis for Workflow Constrained by Resources and Nondetermined Time: An Approach Based on Petri Nets

Time and resource management and verification are two important aspects of workflow management systems. In this paper, we present a modeling and analysis approach for a kind of workflow constrained by resources and nondetermined time based on Petri nets. Different from previous modeling approaches, there are two kinds of places in our model to represent the activities and resources of a workflow, respectively. For each activity place, its input and output transitions represent the start and termination of the activity, respectively, and there are two timing functions in it to define the minimum and maximum duration times of the corresponding activity. Using the constructed Petri net model, the earliest and latest times to start each activity can be calculated. With the reachability graph of the Petri net model, the timing factors influencing the implementation of the workflow can be calculated and verified. In this paper, the sufficient conditions for the existence of the best implementation case of a workflow are proved, and the method for obtaining such an implementation case is presented. The obtained results will benefit the evaluation and verification of the implementation of a workflow constrained by resources and nondetermined time.     

基于链表遍历模式的TCPN映射算法研究

对业务流程的建模分析是建立在工作流网的理论模型上的,因此需要合适的算法将建模工具中用户建立的有向图映射到工作流网.针对经典Petri网的一些固有缺陷,对其在颜色、时间上进行了扩展,给出了赋时着色Petri网定义,并提出了一种基于链表遍历方式的业务流程到工作流网的映射算法.重点研究了工作流模型基本控制结构的映射规则及其相关证明,并给出了该算法的具体实例.     

Dynamic checking of temporal constraints for concurrent workflows

At present, workflow management systems have not sufficiently dealt with the issues of time, involving time modelling at build-time and time management at run-time. They are lack of the ability to support the checking of temporal constraints at run-time. Although some approaches have been devised to tackle this problem, they are limited to a single workflow and use only static techniques to verify temporal constraints. In reality, there are multiple workflows executing concurrently in a workflow management system. There may well exist resource constraints between these concurrent workflows, which affect significantly the verification of temporal constraints at run-time. This paper proposes a novel approach for dynamic verification of temporal constraints for concurrent workflows. We first investigate resource constraints in workflow management systems, and then define concurrent workflow executions. Based on these definitions, we propose a verification method by analysing the temporal relationship and resource constraints between activities among concurrent workflows.     

基于Petri网的保险索赔工作流模型

Petri网是一种有效的形式化建模工具,能自然地描述并发、冲突、同步等系统特性。给出基于Petri网的保险索赔工作流模型,将Petri网三要素以对象的形式描述出来,并对此工作流模型的正确性定义和验证进行了说明。     

An uncoordinated asynchronous checkpointing model for hierarchical scientific workflows

Scientific workflow systems often operate in unreliable environments, and have accordingly incorporated different fault tolerance techniques. One of them is the checkpointing technique combined with its corresponding rollback recovery process. Different checkpointing schemes have been developed and at various levels: task- (or activity-) level and workflow-level. At workflow-level, the usually adopted approach is to establish a checkpointing frequency in the system which determines the moment at which a global workflow checkpoint – a snapshot of the whole workflow enactment state at normal execution (without failures) – has to be accomplished. We describe an alternative workflow-level checkpointing scheme and its corresponding rollback recovery process for hierarchical scientific workflows in which every workflow node in the hierarchy accomplishes its own local checkpoint autonomously and in an uncoordinated way after its enactment. In contrast to other proposals, we utilise the Reference net formalism for expressing the scheme. Reference nets are a particular type of Petri nets which can more effectively provide the abstractions to support and to express hierarchical workflows and their dynamic adaptability.     

基于交互学习的柔性工作流形式化验证方法研究

工作流过程建模是一个复杂且易错的过程，在建模阶段进行有效的过程验证是十分必要的。目前，柔性工作流验证领域的研究还比较欠缺，该文在这方面作了一些探索。把过程合理化验证和化简验证技术应用于基于交互学习的柔性工作流建模的形式化验证中，叙述了需要验证的问题和复杂度。利用Petri网的形式化基础特性对过程进行合理性验证和规约验证。根据规约粒度的不同，分别对基于交互学习的柔性工作流模型进行原子级和组件级规约。规约使用的基本技术有库所融合、变迁融合和子网融合。在特性保持的前提下，将过程模型缩小到适当规模。结果表明，基于交互学习的柔性工作流过程建模中的形式化验证方法具有一定的实用性和可操作性。     

Fuzzy rule base systems verification using high-level Petri nets

In this paper, we propose a Petri nets formalism for the verification of rule-based systems. Typical structural errors in a rule-based system are redundancy, inconsistency, incompleteness, and circularity. Since our verification is based on Petri nets and their incidence matrix, we need to transform rules into a Petri nets first, then derive an incidence matrix from the net. In order to let fuzzy rule-based systems detect above the structural errors, we are presenting a Petri-nets-based mechanism. This mechanism consists of three phases: rule normalization, rules transformation, and rule verification. Rules will be first normalized into Horn clauses, then transform the normalized rules into a high-level Petri net, and finally we verify these normalized rules. In addition, we are presenting our approach to simulate the truth conditions which still hold after a transition firing and negation in Petri nets for rule base modeling. In this paper, we refer to fuzzy rules as the rules with certainty factors, the degree of truth is computed in an algebraic form based on state equation which can be implemented in matrix computation in Petri nets. Therefore, the fuzzy reasoning problems can be transformed as the liner equation problems that can be solved in parallel. We have implemented a Petri nets tool to realize the mechanism presented fuzzy rules in this paper.     

XRL/Woflan: Verification and Extensibility of an XML/Petri-Net-Based Language for Inter-Organizational Workflows

In this paper, we present XRL/Woflan. XRL/Woflan is a software tool using state-of-the-art Petri-net analysis techniques for verifying XRL workflows. The workflow language XRL (eXchangeable Routing Language) supports cross-organizational processes. XRL uses XML for the representation of process definitions and Petri nets for its semantics. XRL is instance-based, therefore, workflow definitions can be changed on the fly and sent across organizational boundaries. These features are vital for today's dynamic and networked economy. However, the features also enable subtle, but highly disruptive, cross-organizational errors. On-the-fly changes and one-of-a-kind processes are destined to result in errors. Moreover, errors of a cross-organizational nature are difficult to repair. XRL/Woflan uses eXtensible Stylesheet Language Transformations (XSLT) to transform XRL specifications to a specific class of Petri nets, and to allow users to design new routing constructs, thus making XRL extensibe. The Petri-net representation is used to determine whether the workflow is correct. If the workflow is not correct, anomalies such as deadlocks and livelocks are reported.     

Soundness of workflow nets: classification, decidability, and analysis

Workflow nets, a particular class of Petri nets, have become one of the standard ways to model and analyze workflows. Typically, they are used as an abstraction of the workflow that is used to check the so-called soundness property. This property guarantees the absence of livelocks, deadlocks, and other anomalies that can be detected without domain knowledge. Several authors have proposed alternative notions of soundness and have suggested to use more expressive languages, e.g., models with cancellations or priorities. This paper provides an overview of the different notions of soundness and investigates these in the presence of different extensions of workflow nets. We will show that the eight soundness notions described in the literature are decidable for workflow nets. However, most extensions will make all of these notions undecidable. These new results show the theoretical limits of workflow verification. Moreover, we discuss some of the analysis approaches described in the literature.