In this paper we discuss how the concept of ontology can be beneficial for the authoring support of Web-based educational systems (WBES). We take a semantic perspective on the knowledge representation within such systems and explore the interoperability between the various ontological structures for domain and instructional modeling and the modeling of the entire authoring process. This work is based on previous research on modeling of application-oriented aspects within two existing web-based systems SmartTrainer [10] and AIMS [2]. Authoring Task Ontology (ATO) is envisioned as main driving mechanism in providing knowledge to the authoring tools and in enabling them to guide, support, navigate and check the consistency and completeness of the authoring activities at all levels of complexity. It provides operational semantics to the authoring process, by means of specification of authoring activities, sub-activities, goals and stages. In the construction of ATO we consider specificatio...