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170 M. Adams and N. Russell
and the exception should be handled, then a handler must be defined and added to
the repertoire.
There is no scenario in which it would make sense for two case instances with
identical contexts to have a particular exception handled in two different ways.
Here, the benefit of automated selection of the handler over manual selection is
twofold: (1) it is vastly more efficient; and (2) manual selection introduces the
capacity for human error – that is, if the case contexts are identical, then it is sim-
ply at the whim of the user as to which handler is selected. Or, to put it another
way, for a decision to be correctly made about the invocation of a certain han-
dler, the decision of whether to choose one handler over another depends directly
on the context of the case instance. It cannot be asserted that two case instances
would require two different handlers if their contexts were identical. It is precisely
the differences in context that define and require differences in exception handling
methods.
In the chapter notes, examples are given of approaches to exception handling;
generally those approaches depend on manual intervention and selection of han-
dlers. It may be said that those kinds of approaches are not context-aware, and thus
the decision making is left to a (human) administrator.
The worklet approach is context-aware, and so the majority of decisions are
system-based, with reference to the context of the case instance. However, within the
Worklet Service manual intervention is required when there is no handler defined
that matches the context of a particular case instance. This is manifested in two
ways: either a handler cannot be matched to the current case context (i.e., a handler
has not yet been defined) or a handler has been returned that is correct for the gen-
eral context but deemed inappropriate because of differences in the context detail. In
both cases, a manual interaction involving a user and an administrator is undertaken
to define a new handler for that particular case instance.
Manual intervention is also required when externally triggered exceptions occur.
In such scenarios, a user is presented with a list of possible exception events, from
which they make a choice.
Therefore, while in the majority of instances manual intervention is not required,
the Worklet Service also provides support for manual intervention in certain scenar-
ios as required.

5.5 Epilogue

While there have been many approaches to exception handling for workflows, most
are built as extensions to an underlying framework that imposes rigidity in process
expression and enactment. Such approaches usually involve a reliance on man-
ual intervention and runtime user interactivity. Thus, they are in opposition to the
perceived gains offered by workflow systems. Users are required to incorporate
“unnatural” actions into their work routines so that their work processes match that
of the workflow specification, or take their work off-system until such time as the