It can be doubted, whether the student is a university's customer, but if he is regarded as such, a campus management system is a very important customer-induced service system. Our paper proposes an incremental ontology-based method for reference models, applied in the domain of German-speaking higher education institutions. The method is applied to gain a reference data model for campus management system systems being deployed since about three years as competing solutions for large universities. The model is developed validating it empirically using publicly available institutions' regulations. An important goal of our paper is, to give the readers of our community basic insights into the construction of an ontology, which is an important foundation of semantic modelling.