Page 223 -

216 M. Adams et al.
Table 7.1 Summary of service actions
Cause Interface Selection Action Returned
work item B Case & item Worklet
enabled context data

Internal X Exception type Exlet
exception and case & item
context data
External – Exception type Exlet
exception and case & item
context data

be on (enabling and disabling an Interface X listening service is achieved via a
parameter setting in a configuration file). Interface X provides the following events:

CheckCaseConstraintEvent: This event is fired when a case begins, and again
when it ends. If there are constraints (in the rule set) associated with the partic-
ular specification, they are checked against the case data. If the constraints are
violated, an appropriate exlet is selected based on the context of the case and/or
work item, and then executed
CheckWorkItemConstraintEvent: This event is fired when a work item is enabled,
and again when it completes, and works in a similar way to the case-level
constraint events
WorkItemAbortException: This event is fired when the processing of a work item
is being performed by an external application and the application fails before
processing is completed
TimeoutEvent: This event occurs when a work item has an invoked timer associ-
ated with it and the deadline set for that work item is reached
ResourceUnavailableException: This event occurs when an attempt has been
made to allocate a work item to a resource and the resource reports that it is
unable to accept the allocation or the allocation cannot otherwise proceed
ConstraintViolationException: This event occurs when a data constraint has
been violated for a work item during its execution (as opposed to pre- or
post-execution)
CaseCancelationEvent: This event is fired when a case is canceled (as opposed
to the CanceledWorkItemEvent of Interface B)

It is through these events that the Exception Service detects exceptions and pro-
vides handling processes for them. Note again that the Engine has no knowledge of
an exception occurring, or of how it is (or is not) handled, but simply announces
milestones in a process instance life-cycle or relays exception triggering events
from other services to the Worklet Exception Service (and/or any other Interface X