Ontologies.conceptualizations of a domain shared by a community of users. play a major role in the Semantic Web, and are increasingly being used in knowledge management systems, e-Science, bio-informatics, and Grid applications. The design, maintenance, reuse, and integration of ontologies are complex tasks. Like software engineers, ontology engineers need to be supported by tools and methodologies that help them to minimize the introduction of errors, i.e., to ensure that ontologies do not have unexpected consequences. In order to develop this support, important notions from software engineering, such as module, black-box behaviour, and controlled interaction, need to be adapted. Recently, there has been growing interest in the topic of modularity in ontology engineering. In this talk I will review recent advances in this area. I will introduce the notions of conservative extension, safety and module. I will discuss the decidability and complexity of the decision problem associated to these notions. Then, I will discuss the development of practical algorithms as well as of methodologies for ontology engineers to use these notions in practice. The talk will also cover aspects of tool design aspects and new research directions for the future.
