Between 2003 and 2008, within the LORNET research network (www.lornet.org), our team has been designing and developing TELOS, an innovative operation system for eLearning and knowledge management environments that is driven by a technical ontology. After presenting the underlying principles of this system, we will develop a graphic model of the resulting ontology that captures the conceptual architecture of the system. Next, we will present the main aggregation modeling tool and the way it is related to the TELOS Ontology. Finally, we will illustrate how the ontology is used to drive the system at run-time. The conclusion will discuss the contri- bution of this research to the field of ontological engineering of software systems.