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Robert Müller. Event-Oriented Dynamic Adaptation of Workflows: Model, Architecture, and Implementation. PhD thesis submitted to Fakultät für Mathematik und Informatik at the Universität Leipzig. Full thesis (PDF).
Abstract
Workflow management is widely accepted as a core technology to
support long-term business processes in heterogeneous and distributed
environments. However, conventional workflow management systems do not
provide sufficient flexibility support to cope with the broad range of
failure situations that may occur during workflow execution. In
particular, most systems do not allow to dynamically adapt a workflow
due to a failure situation, e.g., to dynamically drop or insert
execution steps.
As a contribution to overcome these limitations, this dissertation
introduces the agent-based workflow management system AGENTWORK.
AGENTWORK supports the definition, the execution and, as its
main contribution, the event-oriented and semi-automated dynamic
adaptation of workflows. Two strategies for automatic workflow
adaptation are provided. Predictive adaptation adapts workflow parts
affected by a failure in advance (predictively), typically as soon
as the failure is detected. This is advantageous in many
situations and gives enough time to meet organizational constraints for
adapted workflow parts. Reactive adaptation is typically performed
when predictive adaptation is not possible. In this case,
adaptation is performed when the affected workflow part is to be
executed, e.g., before an activity is executed it is checked
whether it is subject to a workflow adaptation such as dropping,
postponement or replacement. In particular, the following
contributions are provided by AGENTWORK.
A Formal Model for Workflow Definition, Execution, and Estimation:
In this context, AGENTWORK first provides an object-oriented workflow
definition language. This language allows for the definition of
a workflow’s control and data flow. Furthermore, a
workflow’s cooperation with other workflows or
workflow systems can be specified. Second, AGENTWORK provides a
precise workflow execution model. This is necessary, as a running
workflow usually is a complex collection of concurrent activities and
data flow processes, and as failure situations and dynamic
adaptations affect running workflows. Furthermore, mechanisms for
the estimation of a workflow’s future execution behavior are
provided. These mechanisms are of particular importance for
predictive adaptation. Mechanisms for Determining and Processing
Failure Events and Failure Actions: AGENTWORK provides mechanisms
to decide whether an event constitutes a failure situation and what has
to be done to cope with this failure. This is formally achieved by
evaluating event-condition-action rules where the
eventcondition part describes under which condition an event has
to be viewed as a failure event. The action part represents the
necessary actions needed to cope with the failure. To support the
temporal dimension
of events and actions, this dissertation provides a novel
event-condition-action model based on a temporal object-oriented
logic.
Mechanisms for the Adaptation of Affected Workflows: In case of
failure situations it has to be decided how an affected workflow
has to be dynamically adapted on the node and edge level. AGENTWORK
provides a novel approach that combines the two principal
strategies reactive adaptation and predictive
adaptation. Depending on the context of the failure, the
appropriate strategy is selected. Furthermore, control flow
adaptation operators are provided which translate failure actions into
structural control flow adaptations. Data flow operators adapt the
data flow after a control flow adaptation, if necessary.
Mechanisms for the Handling of Inter-Workflow Implications of
Failure Situations: AGENTWORK provides novel mechanisms to decide
whether a failure situation occurring to a workflow affects other
workflows that communicate and cooperate with this workflow. In
particular, AGENTWORK derives the temporal implications of a
dynamic adaptation by estimating the duration that will be needed to
process the changed workflow definition (in comparison with the
original definition). Furthermore, qualitative implications of the
dynamic change are determined. For this purpose, so-called quality
measuring objects are introduced.
All mechanisms provided by AGENTWORK include that users may interact
during the failure handling process. In particular, the user has
the possibility to reject or modify suggested workflow
adaptations. A Prototypical Implementation: Finally, a
prototypical CORBA-based implementation of AGENTWORK is described.
This implementation supports the integration of AGENTWORK into the
distributed and heterogeneous environments of real-world
organizations such as hospitals or insurance business enterprises.
Last changed:
$Date: 2006-03-23 22:48:25 +0000 (Thu, 23 Mar 2006) $ $Revision: 57 $
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