A rule is a database Streams object that
enables the Streams client to perform an action when an event
occurs and a particular condition is met. Rules Engine, which is
built into Streams, evaluates the rules. When the rules are
grouped, they are known as rule sets. Rule sets may be positive
or negative. Stream tasks very much depend on the rules.
Stream Clients such as Capture, Apply, and
Propagation processes utilize the rules to select or discard the
events. For instance, capture rules dictate what events to be
extracted and what events are discarded by a Capture process.
The propagation rules specify dictate what events are to be sent
out what events are discarded by a Propagation process. In the
same way, apply rules determine what dictates, what events have
applied, and what events have to be discarded by an Apply
Each rule has three distinct components:
Rule Condition - The rule condition
combines one or more expressions and conditions and returns a
Boolean value which is a value of TRUE, FALSE or NULL. An
expression is a combination of one or more values and operators.
Rule Evaluation Context - This is an
object that defines external data that can be referenced in the
rule conditions. The external data can exist as variables, table
data, or both.
Rule Action Context - This is
optional information associated with a rule that is interpreted
by the Streams client of the rules engine when the rule is