During the past decade we have developed OCA, an ontology dedicated to complex artifacts. OCA has been applied extensively within the domain of communication systems and has proven a valuable tool for building models of both products and processes. Today, OCA is tightly integrated with a modeling method called MacroModelingTechnique (MMT). OCA-based MMT has increased the effectivness of model building particularly during the early phases of an industrial engineering process where numerous technical and non-technical aspects need to be considered and shared by diverse experts. This paper discusses and assesses the design of OCA. Much of OCA’s design hinges on a technique to construct key concepts in a principled rather than in an ad-hoc manner. In fact, much of OCA’s design is determined by "ontological principles".