IOS Press Guest Editorial Modularity in Ontologies

In the past 10 years, modularity has been established as a central research topic in ontology engineering. Several approaches and techniques have been investigated and developed in detail to characterise and deal with modularity [1]. Theoretical as well as practical aspects of modularity have become essential to the design of ontologies. They aim at reducing complexity, improving maintenance, and support reasoning over modules [2]. However, the field is still highly active and widely accepted solutions are yet to be determined. The 4 articles in this special issue present thoroughly investigated approaches that contribute to modularity in ontologies on quite distinct, but equally important layers, which we will sketch below in more detail. The number of ontologies available nowadays, as well as their size, is steadily increasing. There is a large variation in subject matter, level of specification and detail, intended purpose and application. On-tologies covering several domains at once are often developed in a distributed manner addressing the var-ious aspects, but also such that contributions from distinct sources may be relevant for different parts of a single domain. Not only is it difficult to determine and define interrelations between such distributed ontologies, it is also challenging to reconcile ontologies which might be consistent on their own but jointly inconsistent. Further challenges include extracting the relevant parts of an ontology, re-combining inde