Temporal Perspectives in Event Processing

Introduction to Event Processing

Event denotes something that happens in reality (Luckham, 2002). While data-item typically denotes the state of some entity, events denote transition between these states. There is a semantic overload in the term “event”, since it reflects both the event occurred in the reality and its representation in the computer domain (event message or event object). Event is being processed by the means of “event processing network” (Sharon, 2008).

The life-cycle of event processing application is detailed below (some of it in iterative way):

• 1.

  Event schemas are defined.

• 2.

  Event producers devise mechanism to emit events: in push, periodic pull, or on-demand pull. Event producer examples are: instrumented program, state observer in business process management system, sensors.

• 3.

  The event is published on a channel and routed through an “event pipe” to one or more “event processing agents” which – validate, transform, enrich, filter or detect patterns and create more events that are in turn published on another channel and routed to more event processing agents.

• 4.

  At the edge of the event processing network the created events called “situation events” and are routed to “event consumers”

Figure 1 shows an EPN example, for a monitored patient in the hospital.

Figure 1.

Event processing network example

Event producers are:

• •

  Admittance office that records admittance and release of patients.

• •

  Blood pressure meter

• •

  Fever meter

Agents are performing: filtering, aggregation, enrichment, transformation and pattern detection; routing channels are designated in r1… r9 and event pipes are designated in p1… p20. We shall use this patient monitoring simple example to demonstrate all concepts. The patterns that need to be detected are:

• •

  Ascending Fever: Fever of more than 39 degrees Celsius is consistent over three hours and is constantly ascending, this is calculated every three hours – in 00:00, 03:00, 06:00, 09:00, 12:00, 15:00, 18:00, 21:00.

• •

  Hypotension: The average systolic blood pressure over three consecutive measurements is less than 85

• •

  Ascending Fever and later Hypotension.

• •

  Systolic Blood Pressure is more than 180 and patient is diabetic within the first day after admittance.