|In this work we define a rational extension SROEL-RT of the low complexity description logic SROEL, which underlies the OWL EL ontology language. The logic is extended with a typicality operator T, whose semantics is based on Lehmann and Magidor’s ranked models and allows for the definition of defeasible inclusions. We develop a Datalog materialization calculus for rational entailment in SROEL-RT, showing that instance checking can be computed in polynomial time. Also, we show that deciding instance
checking under minimal entailment is a coNP-hard problem.