Fix OWL 2 DL global restrictions violation #38
Description
The use of the property "usesLanguage" in the definition of the class NativeKnowledgeExpression violates global restrictions on axioms in OWL 2 DL: http://www.w3.org/TR/owl2-syntax/#Global_Restrictions_on_Axioms_in_OWL_2_DL (cardinality restriction on an object property expression that is not simple (because it is subclass of a property chain).