Abstract:Ontologies are an essential component of semantic knowledge bases and applications, and nowadays they are used in a plethora of domains. Despite the maturity of ontology languages, support tools and engineering techniques, the testing and validation of ontologies is a field which still lacks consolidated approaches and tools. This paper attempts at partly bridging that gap, taking a first step towards the extension of mutation testing techniques to ontologies expressed in a widely-used format. Mutation testing techniques, revisited in the light of the peculiar features of the ontology language and structure, can help in the engineering and refinement of ontologies and software based on them.