Additional SOA Patterns –Supporting Composition Controllers - Applied SOA Patterns on the Oracle Platform - page 551

• Rules' validation could be based on the evaluation of XPath expressions. As men-
tioned in the preceding bullet item, performance can be affected negatively here
as well.
Based on these two samples, RE can be briefly described as a mechanism that works on
the already mentioned Event Pattern Language (EPL) semantics and principles. An
EPL-based Rule Engine comprises the following components:
• Components and basic events (as in case 1):
Insert(RName) , Update(RName) , Delete(RName) ; RName is the Ob-
ject Ref
• Simple Event expressions (basic event plus the condition of the basic event, by
default, "ALL"):
evntkind(RName(X), <condition-expression>)
• Actions; they refer to the action performed on the rule. According to architectural
rule 1, you cannot perform backward lookups on RE actions from MB/SB but can
perform forward lookups from BA.
• EPL Modules (MB RE rulesets) or collection of rules. This collection is indexed.
• Any module has two parts: the first is the declaration of the basic monitored
events and the second is a list of rules, which will be applied to the declarative
part. Declaration of basic monitored events is part of the Object Context and
provided by BA. Rules are stored on the MB RE side and linked to the BE code
and associated with BE's basic events:
Begin Ruleset
Begin declaration
Monitor Insert(CARGO)
End declaration
Begin Rule
CompareWith(EventSatisfaction,Apply(valueOf
mhs:< XPath-to-key-element>)
End Rule
End Ruleset
EventSatisfaction -> POD_CODE
where
declarations shall be provided by BA
and