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sets need to be defined (i.e., rules defined within those tree sets). Of course, rules
for other event types can be added later if required. Figure 11.16 shows the Time-
out rule tree for the or Arrange Delivery Appointment task of the Payment subnet
(cf. Sect. 11.7.1).

11.9 Extending the Available Conditionals

The Worklet Service provides a discrete class that enables developers to extend the
set of functions available to be used as part of the conditional expressions of rule
sets. The class is called RdrConditionFunction, the source code for which currently
contains a small number of examples to give developers an indication of the kinds
of things that can be achieved with the class and how to create additional func-
tions. The class is freely extensible into any domain space, and thus data can be
drawn from diverse sources, such as process mining, resource logs, and external
databases, and queried through user-defined functions as part of the evaluation of
the conditional expressions of rule nodes. The ConditionEvaluator class has been
designed to call the RdrConditionFunction object to resolve function references in
conditional expressions to their evaluated values. As the interface between this class
and the rest of the service is very small, it can easily be extended and separately
recompiled, avoiding the overhead of rebuilding the entire service.
The class code is split into four sections:

Header: containing a listing of available functions and a method to test for the
existence of a function
Execute Method: a method called by the ConditionEvaluator object when evalu-
ating a condition containing a user-defined function
Function Definitions: the functions themselves
Implementation: where additional support methods may be created.

Once a function is added, it can be used in any rule’s conditional expression.
One example method of the class is isNotCompleted, which is designed to return a
boolean true value if a work item does not have a completed status.
The objective of the RdrConditionFunction class is to allow developers to easily
extend the capabilities of the Worklet Service by providing the means to test for
things in the conditional expressions of rule nodes other than the process instance’s
data attributes and values. This allows data from any source to be tested during
rule evaluations and also provides the service with ease-of-use capabilities when
formulating new conditions.