The Common Event Infrastructure facilitates
events.
Why and when to perform this task
The
Common Event Infrastructure provides
facilities for the generation, propagation, persistence, and consumption of
events, but it does not define the actual events. When you plan how to use
the event infrastructure in your system design, you need to understand the
business concepts that are relevant, and map them to the appropriate components
of your system design. You should provide the semantics of event management
by defining event types and event groups, in the context of an architecture
of event sources and event consumers.
Steps for this task
- Identify each event source. The event source
is the application that creates the event. The event source passes the event
object to the event infrastructure. The event infrastructure also stores the
event object in a database for later retrieval. The role of the event infrastructure
is to pass the event object onto any applications that express an interest
in receiving it.
- Identify each event consumer. An event consumer
is an application that can use the information that is contained in the event
object. Event consumers typically process events from a number of event sources.
- Identify the hierarchy of the event correlation spheres and
the identifiers for these spheres. Event consumers can use event
correlation spheres to correlate events. The ECSEmitter class supports a hierarchy
of correlation spheres by storing the current identifier and the parent identifier
of the correlation spheres of an event in each event.
Note: ECSEmitter and
correlation sphere capabilities are provided through the Events service and
not through the Common Event Infrastructure,
itself.
For example, a Business Process Execution Language (BPEL)
activity opens a correlation sphere for the current activity that identifies
the activity with the activity instance ID. The parent correlation sphere
is the correlation sphere of the process instance on behalf of which the activity
is run. The parent correlation sphere is identified by the process instance
ID.
- Identify each event group. An event group defines
the characteristics (property values) that all events of interest to a particular
type of consumer can contain. Policies, such as access controls and distribution
rules are assigned to the event groups to customize the behavior of the event
infrastructure for each user group.
Example
WebSphere supplies a default event group that is defined to include
all events. This event group is called Event groups list and has a
Java Naming and Directory Interface (JNDI) name of com/ibm/events/configuration/event-groups/Default
The
following figure shows the relationship between these objects:
Figure 1. The
architecture of an event source (which creates events), an event consumer
(which makes use of the event data), and an event group (which defines the
characteristics and associated policies for each type of event).