Workflow patterns put into context

In his paper ??Approaches to Modeling Business Processes. A Critical Analysis of BPMN, Workflow Patterns and YAWL??, Egon B?rger criticizes the work of the Workflow Patterns Initiative in a rather provocative manner. Although the workflow patterns and YAWL are well established and frequently used, B?rger seems to misunderstand the goals and contributions of the Workflow Patterns Initiative. Therefore, we put the workflow patterns and YAWL in their historic context. Moreover, we address some of the criticism of B?rger by pointing out the real purpose of the workflow patterns and their relationship to formal languages (Petri nets) and real-life WFM/BPM systems.     

Soundness-preserving reduction rules for reset workflow nets

The application of reduction rules to any Petri net may assist in its analysis as its reduced version may be significantly smaller while still retaining the original net’s essential properties. Reset nets extend Petri nets with the concept of a reset arc, allowing one to remove all tokens from a certain place. Such nets have a natural application in business process modelling where possible cancellation of activities need to be modelled explicitly and in workflow management where such process models with cancellation behaviours should be enacted correctly. As cancelling the entire workflow or even cancelling certain activities in a workflow has serious implications during execution (for instance, a workflow can deadlock because of cancellation), such workflows should be thoroughly tested before deployment. However, verification of large workflows with cancellation behaviour is time consuming and can become intractable due to the state space explosion problem. One way of speeding up verification of workflows based on reset nets is to apply reduction rules. Even though reduction rules exist for Petri nets and some of its subclasses and extensions, there are no documented reduction rules for reset nets. This paper systematically presents such reduction rules. Because we want to apply the results to the workflow domain, this paper focusses on reset workflow nets (RWF-nets), i.e. a subclass tailored to the modelling of workflows. The approach has been implemented in the context of the workflow system YAWL.     

Remarks on Egon Börger: “Approaches to model business processes: a critical analysis of BPMN, workflow patterns and YAWL, SOSYM 11:305–318”

Egon Börger (SOSYM, 11, pp. 305–318, 2012) challenges the concepts of BPMN, workflow patterns and YAWL as useful contributions to the modeling of business processes. I show that he misjudges the role of BPMN, YAWL and similar techniques in the modeling of business processes. In particular he mistakes YAWL’s formal basis, i.e. Petri nets. Börger furthermore suggests evaluation criteria for business process modeling tools. I argue that his criteria overemphasize some less important aspects, while ignoring some decisive ones.     

用着色Petri网建模工作流模式

工作流模式指在工作流过程模型中反复出现的过程基本构造,是衡量工作流建模语言在控制流方面的表达能力和适用性的重要标准,目前市场上的工作流引擎对其支持得并不好。本文重点阐述了基于着色Petri网的工作流建模语言对当前流行的20种工作流模式的支持情况。结果表明,该语言不仅能很好地支持全部模式,而且具有建模简洁、准确的特点。同其它建模语言相比,用着色Petri网建模工作流模式具有较好的灵活性和扩展性。它也为如何使基于着色Petri网的工作流引擎能够正确、有效地支持全部20种工作流模式提供了有意义的指导。     

基于Petri网的工作流模式建模及应用

工作流模式建模是工作流模型的基础,Petri网同步器是目前最有效的工作流模型建模方法。使用网和同步距离对工作流模式进行分析,将目前常用的工作流模式归纳成为三种：完全同步、竞争同步、非同步。而Petri网同步器只能表示完全同步,不能表示竞争同步和非同步,为此提出一种改进的同步器,通过改进同步类型,使得同步器可以建模三种同步模式,较之改进前的同步器,增强了建模竞争同步模式和非同步模式的能力。     

The relationship between workflow graphs and free-choice workflow nets

Workflow graphs represent the main control-flow constructs of industrial process modeling languages such as BPMN, EPC and UML activity diagrams, whereas free-choice workflow nets are a well understood class of Petri nets that possesses many efficient analysis techniques. In this paper, we provide new results on the translation between workflow graphs and free-choice workflow nets.We distinguish workflow graphs with and without inclusive Or-logic. For workflow graphs without inclusive logic, we show that workflow graphs and free-choice workflow nets are essentially the same thing. More precisely, each workflow graph and each free-choice workflow net can be brought into an equivalent normal form such that the normal forms are, in some sense, isomorphic. This result gives rise to a translation from arbitrary free-choice workflow nets to workflow graphs.For workflow graphs with inclusive logic, we provide various techniques to replace inclusive Or-joins by subgraphs without inclusive logic, thus giving rise to translations from workflow graphs to free-choice nets. Additionally, we characterize the applicability of these replacements. Finally, we also display a simple workflow graph with an inclusive Or-join, which, in some sense, cannot be replaced. This shows a limitation of translating inclusive logic into free-choice nets and illustrates also a difficulty of translating inclusive logic into general Petri nets.     

基于XML的Petri网流程描述及构造

工作流过程定义可以采用不同的建模方法,由于Petri网有坚实的理论基础和易于使用的图形表示,因而是一种理想的建模和分析工具,XPDL是基于XML技术的工作流过程定义语言。文中提出了六种基本的Petri网流程模块,给出了由Petri网向XPDL转换的方法以及由XPDL构造Petri网的方法。     

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.     

精炼工作流网的行为保持性质

本文定义了工作流网的精炼操作，研究了精炼工作流网的行为保持性质。结果表明精炼工作流网满足行为保持性质，即精炼工作流网的行为与原网和子网行为保持一致。在精炼工作流网行为保持性质的基础上，给出了基于原网语言和子网语言的精炼工作流网的语言刻画。本文结果有助于复杂工作流的设计、建模和验证。     

Well-structured languages

This paper introduces the notion of well-structured language. A well-structured language can be defined by a labelled well-structured transition system, equipped with an upward-closed set of accepting states. That peculiar class of transition systems has been extensively studied in the field of computer-aided verification, where it has direct an important applications. Petri nets, and their monotonic extensions (like Petri nets with non-blocking arcs or Petri nets with transfer arcs), for instance, are special subclasses of well-structured transition systems. We show that the class of well-structured languages enjoy several important closure properties. We propose several pumping lemmata that are applicable respectively to the whole class of well-structured languages and to the classes of languages recognized by Petri nets or Petri nets with non-blocking arcs. These pumping lemmata allow us to characterize the limits in the expressiveness of these classes of language. Furthermore, we exploit the pumping lemmata to strictly separate the expressive power of Petri nets, Petri nets with non-blocking arcs and Petri nets with transfer arcs.     

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。     

基于同步合成的结构复杂Petri网的行为描述

首先分析了一类结构简单的Petri网--S-网的语言性质,得到了它们的行为描述方法.拓展了Petri网同步合成的概念,证明了给定一个结构复杂的Petri网都可通过一组S-网的同步合成运算而得到,并给出了相应的求解算法.引入语言的同步交运算,分析了结构复杂的Petri网与其同步合成子网之间的行为关系,给出了结构复杂Petri网的行为描述算法,为利用网语言分析实际系统的行为特征提供了可靠的理论依据和方法.     

正规语言闭包运算的Petri网构造方法

Petri网语言与Chomsky文法体系之间的关系已有了一些结论,已经证明正规语言是Petri网语言的一个子类。相关文献中给出了一种Petri网子类——恰当终结的标准Petri网,并且已经证明恰当终结的标准Petri网语言与正规语言的等价性。在此基础上,研究了正规表达式中Kleene闭包运算“*”的Petri网构造方法,分别给出了Kleene闭包运算“*”的ε-空标注和无ε-空标注Petri网模型的构造方法。该构造方法可由产生正规语言L的网模型直接得到产生正规语言L*的网模型。证明了对于恰当终结的标准Petri网,正规语言闭包运算“*”的构造是封闭的。     

基于C＋＋的城市报建工作流petri网的算法设计

城市报建工作是一个阳光工程,在信息技术发展的今天,实现城市报建工作的网络化管理,通过建立城市报建工作流的petri网,设计相应的计算机算法来实现计算机程序化管理。文中重点设计了报建审批工作流的Petri网,依据工作流的Petri网,应用C＋＋语言设计报建工作主控模块的算法。     

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。     

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.     

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.     

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.     

规范流网中OR-join任务的语义及使能判定算法

对规范流网中OR-join任务语义及使能判定算法进行了深入研究。首先介绍YAWL语言中与OR-join任务有关的概念,规范流网的有关定义,然后在此基础上定义规范流网关于OR-join任务新的语义;最后提出一种判定规范流网OR-join任务使能的算法,并举例说明算法的正确性和有效性。     

基于Petri网的工作流逻辑化简规则的矩阵表示

Petri网是一种很有效的模型描述语言,尤其适合描述工作流。给出了基于Petri网的工作流逻辑(WF_logic)化简规则,这里则借助矩阵及矩阵运算或矩阵上的初等变换来实现这些化简规则,进而用一个具体的实例进行了验证。