HermiT: A Highly-Efficient OWL Reasoner

HermiT is a new OWL reasoner based on a novel “hypertableau” calculus. The new calculus addresses performance problems due to nondeterminism and model size—the primary sources of complexity in state-of-the-art OWL reasoners. The latter is particularly important in practice, and it is achieved in HermiT with an improved blocking strategy and and an optimization that tries to reuse existing individuals rather than generating new ones. HermiT also incorporates a number of other novel optimizations, such as a more efficient approach to handling nominals, and various techniques for optimizing ontology classification. Our tests show that HermiT is usually much faster than other reasoners when classifying complex ontologies, and it is already able to classify a number of ontologies which no other reasoner has been able to handle.