12.3. Event Meta-Data

Every event has associated meta-data. Typically, the meta-data is automatically added as each event is inserted into working memory. The meta-data defaults can be changed on an event-type basis using the meta-data tags:
  • @role
  • @timestamp
  • @duration
  • @expires
The following examples assume the application domain model includes the following class:

Example 12.3. The VoiceCall Fact Class

/**
 * A class that represents a voice call in 
 * a Telecom domain model
 */
public class VoiceCall {
    private String  originNumber;
    private String  destinationNumber;
    private Date    callDateTime;
    private long    callDuration;          // in milliseconds

    // constructors, getters, and setters
}
@role
The @role meta-data tag indicates whether a given fact type is either a regular fact or an event. It accepts either fact or event as a parameter. The default is fact. 
@role( <fact|event> )

Example 12.4. Declaring VoiceCall as an Event Type

declare VoiceCall
    @role( event )
end
@timestamp
A timestamp is automatically assigned to every event. By default, the time is provided by the session clock and assigned to the event at insertion into the working memory. Events can have their own timestamp attribute, which can be included by telling the engine to use the attribute's timestamp instead of the session clock.
To use the attribute's timestamp, use the attribute name as the parameter for the @timestamp tag. 
@timestamp( <attributeName> )

Example 12.5. Declaring the VoiceCall Timestamp Attribute

declare VoiceCall
    @role( event )
    @timestamp( callDateTime )
end
@duration
JBoss BRMS Complex Event Processing supports both point-in-time and interval-based events. A point-in-time event is represented as an interval-based event with a duration of zero time units. By default, every event has a duration of zero. To assign a different duration to an event, use the attribute name as the parameter for the @duration tag. 
@duration( <attributeName> )

Example 12.6. Declaring the VoiceCall Duration Attribute

declare VoiceCall
    @role( event )
    @timestamp( callDateTime )
    @duration( callDuration )
end
@expires
Events may be set to expire automatically after a specific duration in the working memory. By default, this happens when the event can no longer match and activate any of the current rules. You can also explicitly define when an event should expire. The @expires tag is only used when the engine is running in stream mode. 
@expires( <timeOffset> )
The value of timeOffset is a temporal interval that sets the relative duration of the event. 
[#d][#h][#m][#s][#[ms]]
All parameters are optional and the # parameter should be replaced by the appropriate value.
To declare that the VoiceCall facts should expire one hour and thirty-five minutes after insertion into the working memory, use the following:

Example 12.7. Declaring the Expiration Offset for the VoiceCall Events

declare VoiceCall
    @role( event )
    @timestamp( callDateTime )
    @duration( callDuration )
    @expires( 1h35m )
end

See Also:

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