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Defining the Semantics of Reactive Components in

Event-Driven Workflow Execution with Event Histories

Andreas Geppert, Dimitrios Tombros, Klaus R. Dittrich

Technical Report 97.12
September 1997

Department of Computer Science, University of Zurich
Winterthurerstr. 190, CH-8057 Zurich, Switzerland

Abstract: The definition of exact semantics of workflows and involved processing entities is an open yet urgent problem for most systems. This paper considers the semantics and correctness of event-driven workflow execution by reactive components. The basis for the formalization in our approach is provided by an event history which records all the events generated during the execution of workflows by these components. Based on the formal notion of history, it is possible to determine the semantics of workflow systems as the set of event histories they can generate. It also allows to formalize the semantics of reactive components?and consequently, the semantics of workflows?as well as to check whether their observable behavior is correct.
In addition to the precise understanding of event-driven workflow execution, the formalized notion of event history also serves as the specification of the workflow execution engine. Ultimately, the semantics of reactive components provides the basis for specifying transformation rules used to map these components to the execution level.

Keywords: workflow management, ECA-rules, distributed systems

1 Introduction and Motivation

Workflow management systems (WfMS) [9] are cooperative environments in which multiple distributed processing entities cooperate in order to accomplish tasks (e.g., process an insurance claim). A workflow specification defines the required activities and their execution dependencies, data flows between the activities, and further information such as the assignment of resources to activities. WfMS have to provide the functionality for defining and executing workflows in a distributed heterogeneous environment. However, while many research prototypes and products have been developed, only few provide a formal foundation for the specification and execution of distributed workflows.

Our approach to the specification and execution of workflows is multi-leveled [15]. We separate the high-level (e.g., graphical) specification of workflow types and abstract workflow execution characteristics from an intermediate-level executable representation described with the BROKER/SERVICE MODEL (B/SM) [15]. The resulting system is then directly implemented with the help of a distributed execution framework (event engine - EVE) providing facilities for process event management and history logging, communica-