The paper presents our intermediate results in ontologizing a refined formal representation of environments, events, and happenings elaborated in PSI project. This ontology is used for agent-based modeling of engineering design systems and processes. Our formal approach is inspired by Discrete Event Calculus (DEC). In difference to DEC based on discrete linear time representation, it uses fuzzy time intervals [7]. Our framework also refines classic Event Calculi approaches by introducing explicit formal representations for environments and happenings as well as drawing a clear distinction between events and atomic actions. A reduced version of PSI Environment, Event, and Happening ontology based on crisp representation of time intervals has been implemented as an OWL-DL ontology and is used in PSI Design Process Simulation software. Fuzzy time interval based ontology is also implemented in OWL-DL and will be used in the future software versions.