Reasoning about typicality with low complexity Description Logics: the logic EL+⊥T

We present an extension of the low complexity Description Logic EL+⊥ for reasoning about prototypical properties and inheritance with exceptions. We add to EL+⊥ a typicality operator T, which is intended to select the “most normal” instances of a concept. In the resulting logic, called EL+⊥T, the knowledge base may contain subsumption relations of the form “T(C) is subsumed by P”, expressing that typical C-members have the property P. We show that the problem of entailment in EL+⊥T is in co-NP by proving a small model result.