Event-driven systems are highly depending on the quality of detection and processing of events. Many of complex real-world events cannot be processed by the existing event processing systems because they are too complex to be understood and processed by the systems. Complex events can be inferred from raw primitive events based on their incoming sequence, their syntax and semantics. Usage of ontological knowledge about events and their relationship to other non-event concepts in the application domain, can improve the quality of event processing. In this Ph.D. thesis, I am aiming to address the challenges of adding formalized vocabularies/ontologies and declarative rules to the area of event processing for enabling more intelligent event processors which can understand the senses and semantics of events.