Workflow management systems (WfMSs) have been used to support various types of business processes for more than a decade now. In workflows 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, the underlying workflow system 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. To this end, we present a model that specifies QoS and describe an algorithm and a simulation system in order to compute, analyze and monitor workflow QoS metrics.

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Modeling Quality of Service for Workflows and Web Service Processes

Today‘s workflow management systems (WFMS_s) are only applicable in a secure and safe manner if the business process (BP) to be supported is well-structured and there is no need for ad hoc deviations at run-time. As only few BPs are static in this sense, this significantly limits the applicability of current workflow (WF) technology. On the other hand, to support dynamic deviations from premodeled task sequences must not mean that the responsibility for the avoidance of consistency problems and run-time errors is now completely shifted to the (naive) end user. In this paper we present a formal foundation for the support of dynamic structural changes of running WF instances. Based upon a formal WF model (ADEPT), we define a complete and minimal set of change operations (ADEPT_flex) that support users in modifying the structure of a running WF, while maintaining its (structural) correctness and consistency. The correctness properties defined by ADEPT are used to determine whether a specific change can be applied to a given WF instance or not. If these properties are violated, the change is either rejected or the correctness must be restored by handling the exceptions resulting from the change. We discuss basic issues with respect to the management of changes and the undoing of temporary changes at the instance level. Recently we have started the design and implementation of ADEPT_workflow, the ADEPT workflow engine, which will make use of the change facilities presented in this paper.

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Adept _flex —Supporting Dynamic Changes of Workflows Without Losing Control

https://corescholar.libraries.wright.edu/cgi/viewcontent.cgi?article=2096&context=knoesis

Quality of Service for Workflows and Web Service Processes

Fault tolerance is a key requirement in process support systems (PSS), a class of distributed computing middleware encompassing applications such as workflow management systems and process centered software engineering environments. A PSS controls the flow of work between programs and users in networked environments based on a "metaprogram" (the process). The resulting applications are characterized by a high degree of distribution and a high degree of heterogeneity (properties that make fault tolerance both highly desirable and difficult to achieve). We present a solution for implementing more reliable processes by using exception handling, as it is used in programming languages, and atomicity, as it is known from the transaction concept in database management systems. We describe the mechanism incorporating both transactions and exceptions and present a validation technique allowing to assess the correctness of process specifications.

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Exception handling in workflow management systems

Traditionally, process-ware information systems (PAISs) have focused on the support of predictable and repetitive business processes. Even though respective processes are suited to be fully pre-specified in a process model, flexibility is required to support dynamic process adaptations in case of exceptions. Flexibility is also needed to accommodate the need for evolving business processes and to cope with business process variability. Furthermore, PAISs are increasingly used to support less structured processes which can often be characterized as knowledgeintensive. Processes of this category are neither fully predictable nor repetitive, and therefore cannot be fully pre-specified at build-time. The (partial) unpredictability of these processes also demands a certain amount of looseness. This chapter deals with the flexibility needs of both pre-specified and loosely-specified processes and elicitates requirements for flexible process support in a PAIS. In addition, the chapter discusses PAIS features needed to accommodate flexibility needs in practice like, for example, traceability, business compliance and user support.

Enabling Flexibility in Process-Aware Information Systems

Workflow technology has not yet lived up to its expectations not only because of social problems but also because of technical problems, like inflexible and rigid process specification and execution mechanisms and insufficient possibilities to handle exceptions. The aim of this paper is to present a workflow model which significantly facilitates the design and reliable management of complex business processes supported by an automatic mechanism to handle exceptions. The strength of the model is its simplicity and the application independent transaction facility (advanced control mechanism for workflow units) which guarantees reliable execution of workflow activities.

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The Workflow Activity Model WAMO.

Workflow management systems (WFMSs) are becoming the basic technology for organizations to perform their daily business processes (workflows). A consistent and reliable execution of such processes is crucial for all organizations. The authors claim that this can only be achieved by integrating transactional features-especially "workflow transactions"-into WFMSs. Based on this idea, they discuss in detail advanced workflow recovery concepts which are necessary for the reliable and consistent execution of business processes in the presence of failures and exceptions. Additionally, they distinguish between different workflow types and present adequate recovery concepts for each of them.

http://ieeexplore.ieee.org/iel3/4103/12102/00555004.pdf

Workflow recovery

Workflows management systems support the definition and execution of business processes. While business process reeingeneering tools use time information to simulate and optimize processes, themanagement of time is hardly supported in workflows systems. We introduce a concept for time management for workflows systems. It consists of calculating internal deadlines for all activities within a workflows, checking time constraints and monitoring time at run-time. For the calculation of internal deadlines we extend the netdiagram technique PERT to support the structures usually found in workflows. At run-time this time information is used to pro-acticely avoid time errors and reactively resolve time failures. The concept has been implemented in our prototype workflows management system Panta Rhei.

/pdf/epert-extending-pert-for-workflow-management-systems-3ooh0s7342.pdf

ePERT: extending PERT for workflow management systems

We propose a concept for exception handling in workflow management systems. An exception arises if an activity of the workflow does not deliver the desired results due to continuing system failures, environmental circumstances or inadequacy of a business process in some situation. The concept we propose consists mainly of automatic compensation and pursuing alternatives and integration of semi-automatic at hoc intervention. The goal was to ensure consistent execution of business processes with little extra effort at build time as well as at runtime.

Contributions to Exception Handling in Workflow Management

We present the prototypical workflow management system Panta Rhei which was designed to support various types of workflows in an uniform and elegant way The main characteristics of this system are its flexibility, the lean architecture, the integration in the Web, the transactional features and its support of process management We discuss the basic concepts of the system, its architecture and its implementation

Walter Liebhart

Papers

The Workflow Activity Model WAMO.

Workflow recovery

ePERT: extending PERT for workflow management systems

Contributions to Exception Handling in Workflow Management

The Workflow Management System Panta Rhei