Event condition action (ECA) is a short-cut for referring to the structure of active rules in event-driven architecture and active database systems.
Such a rule traditionally consisted of three parts: This structure was used by the early research in active databases which started to use the term ECA.
In a memory-based rule engine, the condition could be some tests on local data and actions could be updates to object attributes.
In either case, actions could also be calls to external programs or remote procedures.
The equivalent in a memory-based rule engine would be to invoke an external method that caused an external event to trigger another ECA rule.