7.4. Event Processing Modes

Rules engines process facts and rules to provide applications with results. Regular facts (facts with no temporal constraints) are processed independent of time and in no particular order. JBoss BRMS processes facts of this type in cloud mode. Events (facts which have strong temporal constraints) must be processed in real-time or near real-time. JBoss BRMS processes these events in stream mode. Stream mode deals with synchronization and makes it possible for JBoss BRMS to process events.

7.4.1. Cloud Mode

Cloud mode is the default operating mode of JBoss Business Rules Management System.
Running in Cloud mode, the engine applies a many-to-many pattern matching algorithm, which treats the events as an unordered cloud. Events still have timestamps, but there is no way for the rules engine running in Cloud mode to draw relevance from the timestamp because Cloud mode is unaware of the present time.
This mode uses the rules constraints to find the matching tuples, activate, and fire rules.
Cloud mode does not impose any kind of additional requirements on facts; however, because it has no concept of time, it cannot take advantage of temporal features such as sliding windows or automatic life-cycle management. In Cloud mode, it is necessary to explicitly retract events when they are no longer needed.
Certain requirements that are not imposed include the following:
  • No need for clock synchronization since there is no notion of time.
  • No requirement on ordering events since the engine looks at the events as an unordered cloud against which the engine tries to match rules.
Cloud mode can be specified either by setting a system property, using configuration property files, or via the API.
The API call follows: 
import org.kie.api.KieBaseConfiguration;
import org.kie.api.KieServices.Factory;

KieBaseConfiguration config = KieServices.Factory.get().newKieBaseConfiguration();
   config.setOption( EventProcessingOption.CLOUD );
The equivalent property follows: 
drools.eventProcessingMode = cloud

7.4.2. Stream Mode

Stream mode processes events chronologically as they are inserted into the rules engine. Stream mode uses a session clock that enables the rules engine to process events as they occur in time. The session clock enables processing events as they occur based on the age of the events. Stream mode also synchronizes streams of events (so events in different streams can be processed in chronological order), implements sliding windows of interest, and enables automatic life-cycle management.
The requirements for using stream mode are the following:
  • Events in each stream must be ordered chronologically.
  • A session clock must be present to synchronize event streams.

Note

The application does not need to enforce ordering events between streams, but the use of event streams that have not been synchronized may cause unexpected results.
Stream mode can be enabled by setting a system property, using configuration property files, or via the API.
The API call follows: 
import org.kie.api.KieBaseConfiguration;
import org.kie.api.KieServices.Factory;

KieBaseConfiguration config = KieServices.Factory.get().newKieBaseConfiguration();
   config.setOption( EventProcessingOption.STREAM );
The equivalent property follows: 
drools.eventProcessingMode = stream