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Chapter 5
Exception Handling

Michael Adams and Nick Russell

5.1 Overview

Translating abstract concepts and descriptions of business practices and rules into
process models is a far from trivial exercise. Even for highly structured processes
(such as medical and banking environments), it is difficult (if not impossible) to
successfully capture all work activities, and in particular all of the task sequences
possible, in a workflow model, at least not without producing some very complex
models.
In fact, it is because of the discrepancies between real-world activities and for-
mal representations of them that workflow process instances typically experience
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exceptions during their execution. Traditionally, exceptions are understood to be
events that by definition occur rarely. But in a workflow process, an exception can
be described as an event that is deemed to be outside “normal” behavior for that
process. Rather than being an error, it is simply an event that is considered to be
a deviation from the expected control-flow or was unaccounted for in the original
process model. Such events happen frequently in real working environments.
Exceptions are a fundamental part of most organizational processes; in fact, a
substantial proportion of the everyday tasks carried out in a business can be catego-
rized as exception handling work. Consequently, every executing instance of a work
process will be likely to incorporate some deviation from the plan. In this sense, a
work plan can be seen to be just another resource or tool that mediates the activi-
ties of workers towards their objective, rather than a prescriptive blueprint that must
be strictly adhered to. Such deviations from the plan should not be considered as
errors, but as a natural and valuable part of the work activity, which provides the
opportunity for learning and thus evolving the plan for future instantiations.
Historically, exception handling within PAIS has fallen well short, particularly
after execution has commenced. It is assumed that if an exception is expected,

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The focus of this chapter is exception handling at the conceptual level – that is, within the control-
flow, data, and resourcing perspectives.
M. Adams (B )
Queensland University of Technology, Brisbane, Australia

A.H.M. ter Hofstede et al. (eds.), Modern Business Process Automation, 147
DOI 10.1007/978-3-642-03121-2 5, c Springer-Verlag Berlin Heidelberg 2010