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• Define acceptable rule operations and implement the handler for them (=, >, <, !,
=, and so on).
• Define supported rule aggregations (weak and strong, that is AND, OR, respect-
ively) and implement the aggregation handler accordingly.
It is quite obvious that the implementation of Rule Centralization does not require the
presence of the single rule engine. Only the rulesets storage will be common (and prefer-
ably, ER-based). Following the steps from the preceding bullet points, it is probable, and
sometimes desirable, to implement RE in several key points of the infrastructure—in the
ESB layer for rule-based routing and invocation and in DB for functional Audit and KPI
evaluation. The latter is related to the operational policy and for its monitoring, rules are
essential. Thus, we will place the policy entity close to the rules definitions.
Event
The implementation of an event's taxonomy is also straightforward. We just have to re-
flect our understanding that the event is the change of an object's state, the object exists
within the application (service or composition), and from the whole enterprise application
prospective, the event could be seen as a primitive (basic) or enterprise (complex). Events
filtering and recognition is the task for the Rule Engine, which is usually inside the north-
bound adapter layer.
The event is part of the Message Header structure, together with three other mandatory
elements, and the key part of composition coordination and context management. The
biggest part of this management is apprehended by the message elements and recognition
is the task for the rule engine.
Message
A business message is a serialized business object. In terms of Service Brokering, it is
presented as an
Enterprise Business Object (EBO)
XSD in the CDM stack. This is an
actual payload, but we need to define and implement other essential parts of a Message
Container to make agnostic service brokering possible. We have already mentioned two of
them:
Message Header (MH)
and the composition execution plan. What other possible
moving parts of the Message Container do you see in the following figure?
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