In this, the 4th and final episode of a series of articles exploring the principles of ontological modelling, the Ontology Working Group (OWG) builds on previous episodes, introducing some new terms from the Unified Foundation Ontology (UFO) and expanding further on the worked example relating to flights and flight planning. With these articles, the OWG aims to make the topic more accessible through a series of connected newsletter articles. Each episode expands on ontological aspects and, by the end, will hopefully provide the reader with enough knowledge to read and contribute to models in the future.