Because it is difficult to engineer a complex ontology with time, we here consider a method that allows for factorizing the complexity of the engineering process, FONTE (Factorizing ONTology Engineering complexity). FONTE divides the engineering task into building a time-less domain ontology and a temporal theory independently from each other. FONTE provides an operator ⊗ that assembles the two independently developed ontologies into the targeted ontology. We investigate the quality of the proposed operator ⊗ by applying it to a practical case study, viz. the engineering of an ontology about researchers including temporal interactions. Categories and Subject Descriptors: I.2.4 Knowledge Representation Formalisms and Methods