This paper proposes a new approach to associating rules with events in object-oriented database systems. In it we propose a new run time mechanism, which associates rules with specific event definitions. This provide a basis for indexing rules by event definitions, which reduces rule checking to a minimum. The proposed subscription mechanism is general, in that it can be applied to both primitive events and composite events. Both rules and events are represented as first class objects. This architecture has been adopted in the ACOOD2 prototype on top of ONTOS.