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11 The Worklet Service 313
The rule set for each specification is stored as XML data in a discrete disk file.
All rule set files are stored in the Worklet Repository.
Thus, the hierarchy of a Worklet Rule Set is (from the bottom up) are:

Rule Node: contains the details (condition, conclusion, id, parent, and so on) of
one discrete rule
Rule Tree: consists of a number of rule nodes conceptually linked in a binary tree
structure
Tree Set: a set of one or more rule trees. Each tree set is specific to a particular
rule type (Timeout, ExternalTrigger, etc.). The tree set of a case-level exception
rule type will contain exactly one tree. The tree set of an item-level rule type will
contain one rule tree for each task of the specification that has rules defined for
it (not all tasks in the specification need to have a rule tree defined)
Rule Set: a set of one or more tree sets representing the entire set of rules defined
for one specification. Each rule set is specific to a particular specification. A rule
set will contain one tree set for each rule type for which rules have been defined.
It is not necessary to define rules for all eight exception/selection types for each
specification, only for those types that are required to be handled; the occurrence of
any exception types that are not defined in the rule set file are simply ignored. So,
for example, if an analyst is interested only in capturing pre- and post-constraints
at the work item level, then only the ItemPreConstraint and ItemPostConstraint tree

Fig. 11.16 Example rule tree (TimeOut tree for Arrange Delivery Appointment task of the
Payment subnet)