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.     

On verification of nested workflows with extra constraints: From theory to practice

Workflows are used to formally describe processes of various types such as business and manufacturing processes. One of the critical tasks of workflow management is automated discovery of possible flaws in the workflow – workflow verification. In this paper, we formalize the problem of workflow verification as the problem of verifying that there exists a feasible process for each task in the workflow. This problem is tractable for nested workflows that are the workflows with a hierarchical structure similar to hierarchical task networks in planning. However, we show that if extra synchronization, precedence, or causal constraints are added to the nested structure, the workflow verification problem becomes NP-complete. We present a workflow verification algorithm for nested workflows with extra constraints that is based on constraint satisfaction techniques and exploits an incremental temporal reasoning algorithm. We then experimentally demonstrate efficiency of the proposed techniques on randomly generated workflows with various structures and sizes. The paper is concluded by notes on exploiting the presented techniques in the application FlowOpt for modeling, optimizing, visualizing, and analyzing production workflows.     

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.     

Towards the construction of workflow-suitable conceptual modelling techniques

Despite their high-level and graphical nature, workflow specifications require a significant amount of implementation detail — for example application programming interface, database access and programming mechanisms for information flow — for a more comprehensive validation than is currently possible. This is currently recognized as a deficiency in workflow conceptualization. Although conceptual modelling techniques are available which are expressive, comprehensive and precise enough, we believe, their concepts and features are not specialized enough for workflow domains. In this paper, we offer a comparative insight into techniques which characterize different aspects and approaches of workflow specifications. These are: structured process modelling, object-oriented modelling, behavioural process modelling and business-oriented modelling. In particular, we determine gaps for workflows capturing operational business transaction processing, for example those of insurance claims, bank loans and government-related registration. For technique construction, we describe five workflow suitability principles.     

SEAM: A state-entity-activity-model for a well-defined workflowdevelopment methodology

Current conceptual workflow models use either informally defined conceptual models or several formally defined conceptual models that capture different aspects of the workflow, e.g., the data, process, and organizational aspects of the workflow. To the best of our knowledge, there are no algorithms that can amalgamate these models to yield a single view of reality. A fragmented conceptual view is useful for systems analysis and documentation. However, it fails to realize the potential of conceptual models to provide a convenient interface to automate the design and management of workflows. First, as a step toward accomplishing this objective, we propose SEAM (State-Entity-Activity-Model), a conceptual workflow model defined in terms of set theory. Second, no attempt has been made, to the best of our knowledge, to incorporate time into a conceptual workflow model. SEAM incorporates the temporal aspect of workflows. Third, we apply SEAM to a real-life organizational unit's workflows. In this work, we show a subset of the workflows modeled for this organization using SEAM. We also demonstrate, via a prototype application, how the SEAM schema can be implemented on a relational database management system. We present the lessons we learned about the advantages obtained for the organization and, for developers who choose to use SEAM, we also present potential pitfalls in using the SEAM methodology to build workflow systems on relational platforms. The information contained in this work is sufficient enough to allow application developers to utilize SEAM as a methodology to analyze, design, and construct workflow applications on current relational database management systems. The definition of SEAM as a context-free grammar, definition of its semantics, and its mapping to relational platforms should be sufficient also, to allow the construction of an automated workflow design and construction tool with SEAM as the user interface     

From Contracts to E-Contracts: Modeling and Enactment

Contracts are complex to understand, represent and process electronically. Usually, contracts involve various entities such as parties, activities and clauses. An e-contract is a contract modeled, specified, executed and enacted (controlled and monitored) by a software system (such as a workflow system). Workflows are used to automate business processes that govern adherence to the e-contracts. E-contracts can be mapped to inter-related workflows, which have to be specified carefully to satisfy the contract requirements. Most workflow models do not have the capabilities to handle complex inter/intra relationships among entities in e-contracts. An e-contract does not adhere to activity/task oriented workflow processes, thus generating a gap between a conceptual model of e-contract and workflow. In this paper, we describe conceptual modeling of e-contracts and present a business process model for e-contract enactment. The enactment of e-contracts necessitates dynamic generation and initiation of workflows during the e-contract execution, besides the static workflows. ER^EC business process model facilitates an integrated approach to e-contracts enactment. Our methodology is illustrated by means of a case study conducted using Financial Messaging Solution contract for banking transactions.     

WIRES: A Methodology for Developing Workflow Applications

Workflow management systems are becoming a relevant support for a large class of business applications, and many workflow models as well as commercial products are currently available. While the large availability of tools facilitates the development and the fulfilment of customer requirements, workflow application development still requires methodological guidelines that drive the developers in the complex task of rapidly producing effective applications. In fact, it is necessary to identify and model the business processes, to design the interfaces towards existing cooperating systems, and to manage implementation aspects in an integrated way. This paper presents the WIRES methodology for developing workflow applications under a uniform modelling paradigm – UML modelling tools with some extensions – that covers all the life cycle of these applications: from conceptual analysis to implementation. High-level analysis is performed under different perspectives, including a business and an organisational perspective. Distribution, interoperability and cooperation with external information systems are considered in this early stage. A set of “workflowability” criteria is provided in order to identify which candidate processes are suited to be implemented as workflows. Non-functional requirements receive particular emphasis in that they are among the most important criteria for deciding whether workflow technology can be actually useful for implementing the business process at hand. The design phase tackles aspects of concurrency and cooperation, distributed transactions and exception handling. Reuse of component workflows, available in a repository as workflow fragments, is a distinguishing feature of the method. Implementation aspects are presented in terms of rules that guide in the selection of a commercial workflow management system suitable for supporting the designed processes, coupled with guidelines for mapping the designed workflows onto the model offered by the selected system.     

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.     

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.     

Specification and validation of process constraints for flexible workflows

Workflow systems have traditionally focused on the so-called production processes which are characterized by pre-definition, high volume, and repetitiveness. Recently, the deployment of workflow systems in non-traditional domains such as collaborative applications, e-learning and cross-organizational process integration, have put forth new requirements for flexible and dynamic specification. However, this flexibility cannot be offered at the expense of control, a critical requirement of business processes.In this paper, we will present a foundation set of constraints for flexible workflow specification. These constraints are intended to provide an appropriate balance between flexibility and control. The constraint specification framework is based on the concept of “pockets of flexibility” which allows ad hoc changes and/or building of workflows for highly flexible processes. Basically, our approach is to provide the ability to execute on the basis of a partially specified model, where the full specification of the model is made at runtime, and may be unique to each instance.The verification of dynamically built models is essential. Where as ensuring that the model conforms to specified constraints does not pose great difficulty, ensuring that the constraint set itself does not carry conflicts and redundancy is an interesting and challenging problem. In this paper, we will provide a discussion on both the static and dynamic verification aspects. We will also briefly present Chameleon, a prototype workflow engine that implements these concepts.     

基于控制关系和数据关系的科学工作流验证

面向科学问题求解的科学工作流具有以数据为中心的特性,其验证要求同时考虑控制流和数据流的合理性。为此,分析科学工作流中的4种控制关系和2种数据关系,给出相关合理性定义,提出相应算法以遍历获得科学工作流中存在的控制关系和数据关系,实现对科学工作流的合理性验证。通过正反实例证明了该验证方法的有效性。     

A schema aware ETL workflow generator

Extract, Transform and Load (ETL) processes organized as workflows play an important role in data warehousing. As ETL workflows are usually complex, various ETL facilities have been developed to address their control-flow process modeling and execution control. To evaluate the quality of ETL facilities, Synthetic ETL workflow test cases, consisting of control-flow and data-flow aspects are needed to check ETL facility functionalities at construction time and to validate the correctness and performance of ETL facilities at run time. Although there are some synthetic workflow and data set test case generation approaches existed in literatures, little work is done to consider both aspects at the same time specifically for ETL workflow generators. To address this issue, this paper proposes a schema aware ETL workflow generator with which users can characterize their ETL workflows by various parameters and get ETL workflow test cases with control-flow of ETL activities, complied schemas and associated recordsets. Our generator consists of three steps. First, with type and ratio of individual activities and their connection characteristic parameter specification, the generator will produce ETL activities and form ETL skeleton which determine how generated activities are cooperated with each other. Second, with schema transformation characteristic parameter specification, e.g. ranges of numbers of attributes, the generator will resolve attribute dependencies and refine input/output schemas with complied attributes and their data types. In the last step, recordsets are generated following cardinality specifications. ETL workflows in specific patterns are produced in the experiment in order to show the ability of our generator. Also experiments to generate thousands of ETL workflow test cases in seconds have been done to verify the usability of the generator.     

Quality of service for workflows and web service processes

Workflow management systems (WfMSs) have been used to support various types of business processes for more than a decade now. In workflows or Web processes for e-commerce and Web service applications, suppliers and customers define a binding agreement or contract between the two parties, specifying quality of service (QoS) items such as products or services to be delivered, deadlines, quality of products, and cost of services. The management of QoS metrics directly impacts the success of organizations participating in e-commerce. Therefore, when services or products are created or managed using workflows or Web processes, the underlying workflow engine must accept the specifications and be able to estimate, monitor, and control the QoS rendered to customers. In this paper, we present a predictive QoS model that makes it possible to compute the quality of service for workflows automatically based on atomic task QoS attributes. We also present the implementation of our QoS model for the METEOR workflow system. We describe the components that have been changed or added, and discuss how they interact to enable the management of QoS.     

Model-as-you-go: An Approach for an Advanced Infrastructure for Scientific Workflows

Most of the existing scientific workflow systems rely on proprietary concepts and workflow languages. We are convinced that the conventional workflow technology that is established in business scenarios for years is also beneficial for scientists and scientific applications. We are therefore working on a scientific workflow system based on business workflow concepts and technologies. The system offers advanced flexibility features to scientists in order to support them in creating workflows in an explorative manner and to increase robustness of scientific applications. We named the approach Model-as-you-go because it enables users to model and execute workflows in an iterative process that eventually results in a complete scientific workflow. In this paper, we present main ingredients of Model-as-you-go, show how existing workflow concepts have to be extended in order to cover the requirements of scientists, discuss the application of the concepts to BPEL, and introduce the current prototype of the system.     

An Evaluation of the Cost and Performance of Scientific Workflows on Amazon EC2

Workflows are used to orchestrate data-intensive applications in many different scientific domains. Workflow applications typically communicate data between processing steps using intermediate files. When tasks are distributed, these files are either transferred from one computational node to another, or accessed through a shared storage system. As a result, the efficient management of data is a key factor in achieving good performance for workflow applications in distributed environments. In this paper we investigate some of the ways in which data can be managed for workflows in the cloud. We ran experiments using three typical workflow applications on Amazon’s EC2 cloud computing platform. We discuss the various storage and file systems we used, describe the issues and problems we encountered deploying them on EC2, and analyze the resulting performance and cost of the workflows.     

A policy enforcement framework for verification and control of service collaboration

This paper proposes a policy enforcement framework to dynamically verify and control the collaboration process in Service-Oriented Architecture (SOA). Dynamic SOA collaboration is different from traditional service collaboration where the workflow is pre-defined at design time while the services used can be discovered at runtime. In dynamic collaboration, both the workflows and services can be determined at runtime. As they will be determined at runtime, many verification activities can be performed at runtime. This paper proposes a dynamic policy enforcement framework that follows the dynamic SOA collaboration process to ensure that various system constraints can be enforced at runtime. The framework includes a policy specification language, a policy completeness and consistency checking, and distributed policy enforcement. Finally, this paper presents the construction of a sample example to illustrate these features with quantitative performance data.     

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.