OMERO events and provenance

What is an event?

As described under OmeroContext, each method call takes place within a single application context (always the same), session, and event. Of these, only event is guaranteed to be unique for every task*. The https://github.com/ome/omero-server/blob/v5.7.0/src/main/java/ome/security/basic/EventHandler.java is responsible for creating new events.

Events as audit log

On each Database-update (INSERT/UPDATE/DELETE), an EventLog is created by a HibernateInterceptor which is then saved to the database at the end of the method call (in UpdateImpl).

Relationship to ModuleExecutions

The OMERO Event plays a similar role to the ModuleExecution in the OME 2 system. They both contain time of create/update/deletion, status, and type information. Event, however, has lost its ACL/permissions role. These values have been moved to embedded values represented by the Details object. Event also is not linked to all the created SemanticTypes as was ModuleExecution, and so cannot fully represent the provenance data needed by the AnalysisEngine. At such time as the AnalysisEngine is ported to Java, the ModuleExecution object will have to be added.

* Here we say “task” and not method call, because all method calls to a single stateful service instance belong to the same event. This is the nature of a stateful service. Logically, however, it is a single action.