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 background knowledge about events and their relationship to other non-event concepts can improve the quality of event processing. In this paper, we discuss the profits and problems of ontology developing and usage in the area of event processing and propose modular upper-level ontologies for semantic enabled complex event processing. We discuss, why the modularity is needed and how these ontologies should be modular build up based on ontology engineering aspects to be able to address scalability, expressiveness and reuse.