From OpenNMS

The acronymn, UEI, represents the OpenNMS term Unique Event Identifier. A UEI is assigned to to each Event in OpenNMS including these generated by Traps. For example, the OpenNMS "Node Lost Service" event has the UEI: value equal to "uei.opennms.org/nodes/nodeLostService".

The UEI quickly becomes a well-known term to the OpenNMS administrator when manually creating Notifications and Alarms as well as when configuring Traps in the Event configuration files.

These UEIs stitch togther the fabric of OpenNMS' publish and subscribe event system. OpenNMS services register with the event system using the UEI in a class commonly often called "BroadcastEventProcessor.java". (Note: Major refactoring is happing in the unstable branch on the services to remove different code smells such as duplication of code, often found in the BroadcastEventprocessor classes. The Spring Framework is being leveraged to do this as well as to simplify our JMX implementation and managing/monitoring of the OpenNMS framework itself.