Automating correctness verification of artifact-centric business process models

ContextThe artifact-centric methodology has emerged as a new paradigm to support business process management over the last few years. This way, business processes are described from the point of view of the artifacts that are manipulated during the process.ObjectiveOne of the research challenges in this area is the verification of the correctness of this kind of business process models where the model is formed of various artifacts that interact among them.MethodIn this paper, we propose a fully automated approach for verifying correctness of artifact-centric business process models, taking into account that the state (lifecycle) and the values of each artifact (numerical data described by pre and postconditions) influence in the values and the state of the others. The lifecycles of the artifacts and the numerical data managed are modeled by using the Constraint Programming paradigm, an Artificial Intelligence technique.ResultsTwo correctness notions for artifact-centric business process models are distinguished (reachability and weak termination), and novel verification algorithms are developed to check them. The algorithms are complete: neither false positives nor false negatives are generated. Moreover, the algorithms offer precise diagnosis of the detected errors, indicating the execution causing the error where the lifecycle gets stuck.ConclusionTo the best of our knowledge, this paper presents the first verification approach for artifact-centric business process models that integrates pre and postconditions, which define the behavior of the services, and numerical data verification when the model is formed of more than one artifact. The approach can detect errors not detectable with other approaches.     

基于图形展开及图形归约的过程模型验证方法

工作流过程模型是业务过程的形式化定义，在业务过程的分析、运行和重组方面起着关键性的作用．为了实现预期的业务目标，需要正确地定义工作流过程模型，它的正确性直接影响业务目标的实现，WfMS开始调度执行之前必须对其进行分析．针对大规模复杂应用的特点和业务过程执行的实际需要，对复杂工作流过程模型的正确性验证进行了研究；基于有向有环图(DCG图)详细讨论工作流过程模型的局部错误以及过程逻辑错误；给出了过程建模中避免错误的相关约束规则；另外了提出了一种新型的图形归约和图形展开相结合的验证方法及过程模型验证算法．     

Defining the resource perspective in the development of processes-aware information systems

ContextThe resource perspective has impact on the performance of business processes. However, current Workflow Management Systems (WfMSs) provide disparate support to its implementation and business process modeling languages provide limited capabilities for its definition. Thus, it is difficult to specify requirements regarding this perspective and to select an appropriate WfMS to support them in order to obtain a technological solution aligned with the organizational needs.ObjectiveTo provide support to the definition, implementation, verification and validation of resource perspective requirements in the development of Process-Aware Information Systems (PAISs) based on WfMSs.MethodThe following activities were carried out: (i) identification of resource perspective aspects in executable workflow specifications, (ii) analysis of the elements provided by the BPMN modeling language to represent these aspects, (iii) development of a framework based on BPMN for defining and implementing these aspects by using the extension mechanism provided by this language, (iv) development of a model-driven development method that leverages the framework to develop PAISs, and (v) validation of the proposed framework and method through the development of a tool supporting them, a case study, and the evaluation against the Workflow Resource Patterns.ResultsA framework, a method and a tool that support the definition of the resource perspective in the development of PAISs.ConclusionBy using the proposed framework and method, practitioners are able to: define the resource perspective requirements in conceptual process models, select a WfMS as implementation platform, and define the implementation of these requirements maintaining the consistency between the conceptual process models and the workflow specifications.     

Context aware exception handling in business process execution language

ContextFault handling represents a very important aspect of business process functioning. However, fault handling has thus far been solved statically, requiring the definition of fault handlers and handling logic to be defined at design time, which requires a great deal of effort, is error-prone and relatively difficult to maintain and extend. It is sometimes even impossible to define all fault handlers at design time.ObjectiveTo address this issue, we describe a novel context-aware architecture for fault handling in executable business process, which enables dynamic fault handling during business process execution.MethodWe performed analysis of existing fault handling disadvantages of WS-BPEL. We designed the artifact which complements existing statically defined fault handling in such a way that faults can be defined dynamically during business process run-time. We evaluated the artifact with analysis of system performance and performed a comparison against a set of well known workflow exception handling patterns.ResultsWe designed an artifact, that comprises an Observer component, Exception Handler Bus, Exception Knowledge Base and Solution Repository. A system performance analysis shows a significantly decreased repair time with the use of context aware activities. We proved that the designed artifact extends the range of supported workflow exception handling patterns.ConclusionThe artifact presented in this research considerably improves static fault handling, as it enables the dynamic fault resolution of semantically similar faults with continuous enhancement of fault handling in run-time. It also results in broader support of workflow exception handling patterns.     

Correct transformation: From object-based graph grammars to PROMELA

Model transformation is an approach that, among other advantages, enables the reuse of existing analysis and implementation techniques, languages and tools. The area of formal verification makes wide use of model transformation because the cost of constructing efficient model checkers is extremely high. There are various examples of translations from specification and programming languages to the input languages of prominent model checking tools, like SPIN. However, this approach provides a safe analysis method only if there is a guarantee that the transformation process preserves the semantics of the original specification/program, that is, that the transformation is correct. Depending on the source and/or target languages, this notion of correctness is not easy to achieve. In this paper, we tackle this problem in the context of Object-Based Graph Grammars (OBGG). OBGG is a formal language suitable for the specification of distributed systems, with a variety of tools and techniques centered around the transformation of OBGG models. We describe in details the model transformation from OBGG models to PROMELA, the input language of the SPIN model checker. Amongst the contributions of this paper are: (a) the correctness proof of the transformation from OBGG models to PROMELA; (b) a generalization of this process in steps that may be used as a guide to prove the correctness of transformations from different specification/programming languages to PROMELA.     

基于并行状态自动机的工作流建模

为了实现工作流管理功能，首先要把业务过程从观实世界抽象出来，并用一种形式化疗法对其进行描述，其结果就是工作流模型。该文讨论利用并行自动机对工作流的形式化问题。基于对工作流和并行自动机的分析，提出了将工作流的概念映射到并行自动机概念上的方法，该方法可以把工作流联盟提出的工作流的4种结构映射到并行自动机的结构上。给出了并行自动机的结点转化图，即给出了工作流引擎的框架。并行自动机是一种图形的、数学化的计算模型，当工作流的模型一并行自动机建立起来后，为工作流的静态特性和动态特性的分析打下不坚实的基础，为进一步的研究作好了准备。     

基于Petri网的工作流过程验证方案的研究

工作流管理系统最主要的功能是要能够对业务流程的变化做出有效的反应。然而,当前的工作流管理系统并不能灵活应对业务流程的频繁变化,因为它们对所建的工作流模型几乎没有任何检查,以保证一些最低限度的正确性。本文结合Petri网相关理论技术,提出一种将过程模型验证机制集成到工作流流程定制组件中的方法,并对所采用的验证方案进行阐述。     

Verifying Object-based Graph Grammars

The development of concurrent and reactive systems is gaining importance since they are well-suited to modern computing platforms, such as the Internet. However, the development of correct concurrent and reactive systems is a non-trivial task. Object-based graph grammar (OBGG) is a visual formal language suitable for the specification of this class of systems. In previous work, a translation from OBGG to PROMELA (the input language of the SPIN model checker) was defined, enabling the verification of OBGG models using SPIN. In this paper we extend this approach in two different ways: (1) the approach for property specification is improved, enabling to prove properties not only about possible OBGG derivations, but also about the internal state of involved objects; (2) an approach is defined to interpret PROMELA races as OBGG derivations, generating graphical counter-examples for properties that are not true for a given OBGG model. Another contribution of this paper is (3) the definition of a method for model checking partial systems (isolated objects or a set of objects) using an assume-guarantee approach. A gas station system modeled with OBGGs is used to illustrate the contributions.This work is partially sponsored by projects IQ-MObile (CNPq-Brazil/CNR-Italy) and PLATUS (CNPq).Osmar Marchi dos Santos is partially sponsored by CAPES-Brazil.     

Timing constraint workflow nets for workflow analysis

The analysis of the correctness and rationality of a workflow model plays an important role in the research of workflow techniques and successful implementation of workflow management. This paper points out the relevant problems in the verification and analysis of a workflow model. It discusses two important properties: schedulability and boundedness of a workflow model considering timing constraints. To specify the timing constraints, WorkFlow net is extended with time information, leading to timing constraint workflow net (TCWF-net). This paper presents a model mapping method to convert a directed network graph (DNG) based workflow model, which is built by a graphic process modeling language extended with time information, into a TCWF-net. It then discusses its schedulability verification and synthesis. An algorithm to decompose an acyclic and free-choice TCWF-net into a set of T-components is presented, followed by a boundedness verification method. The usefulness of the research results is illustrated by an example.     

跨组织多业务事务建模与验证方法

面向服务的事务处理是保障业务交互和协作正确性的关键技术.针对跨组织多业务流程,提供了一种支持多业务事务建模与验证的方法.在建模方法上,对Pi-演算扩展了事务语义,将进程间的动作交互与跨组织膜活动相关联来刻画多业务事务协调行为.在验证过程中,基于等价自动机转换思路集成现有模型检验技术,验证多业务事务是否满足人们需要的各种性质.实验结果表明,该建模与验证方法能够有效地保障多业务流程在设计与实现过程中的正确性.     

An automated approach for merging business process fragments

In the field of business process management, adopting efficient building strategies can improve the quality of companies’ business processes. The reuse of existing business processes or even fragments of them is a practical approach to build complete business processes or coarser-grained process fragments. In the present paper, we deal with the merge of a set of business process fragments for the construction of new complete processes. Our merge mechanism relies on a particular path matrix, that we call gateway path matrix. We use gateway path matrices to represent business process fragments to systematically compose shared components with individual ones. Moreover, our approach ensures that the resulting business process fragments subsume the behavior of initial ones and allows for adding new execution scenarios while controlling undesirable ones. In fact, we detect newly generated behaviors, and alert process designers of undesirable ones through behavioral constraints. We provide extensive experimental results derived from an implementation of our approach applied on a well-known industrial library of business process fragments.     

事务工作流模型定义及完全性分析

事务工作流模型可被视为扩展的事务模型和通用工作流模型的交汇点，提出将工作流的模型定义同其事务属性的定义独立开来，尽管在此方法中区分了多重的事务属性。提出了直观的注解符来定义原子性，提供了一个通用规则——放宽的完全性准则，以适应现实运行中事务管理的需要，以一个网上电子书店工作流应用为例来阐明这种思路。     

工作流模型及其形式化描述

工作流是一个业务过程的全部或部分自动执行．为了实现工作流管理功能，我们必须将业务过程从现实世界中抽象出来，并用一种形式化方法对其进行描述，其结果称为是工作流模型．该文主要讨论工作流模型及其形式化描述问题．基于对现实世界业务过程的分析，该文提出一个三维工作流模型，它包含3个子模型：组织模型、数据模型和过程模型，分别从不同的侧面描述工作流的各种属性．文中详细论述各个子模型及其相互关系，并给出三维工作流模型的形式化描述．     

流程业务化定制中的工作流建模方法研究

针对流程业务化定制的需求,提出了一套面向业务人员的、直观易用的工作流建模方法.首先定义了一种基于有向图的工作流模型.在该模型的基础上,通过设置建模规则来规范业务人员的建模行为,使得无需模型验证就能够保证所建过程模型的正确性,从而回避了传统的有向图方法在模型分析方面的缺陷.最后将这套建模方法转化为Petri网的形式来描述,并利用Petri网的分析技术证明了该方法的可靠性.     

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.     

Applying Propositional Logic to Workflow Verification

The increasing complexity of business processes in the era of e-business has heightened the need for workflow verification tools. However, workflow verification remains an open and challenging research area. As an indication, most of commercial workflow management systems do not yet provide workflow designers with formal workflow verification tools. We propose a logic-based verification method that is based on a well-known formalism, i.e., propositional logic. Our logic-based workflow verification approach has distinct advantages such as its rigorous yet simplistic logical formalism and its ability to handle generic activity-based process models. In this paper, we present the theoretical framework for applying propositional logic to workflow verification and demonstrate that logic-based workflow verification is capable of detecting process anomalies in workflow models.     

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.