Addressed issue #25.

ontology/saref4ehaw.ttl

@@ -1049,6 +1049,7 @@ s4ehaw:Helper rdf:type owl:Class ;
 
 ###  https://saref.etsi.org/saref4ehaw/Impairment
 s4ehaw:Impairment rdf:type owl:Class ;
+                  rdfs:subClassOf saref:State ;
                   rdfs:comment "Defined for users (that can in particular be patients) impairments modelling, e.g. aural impairment, skeletal impairment, ocular impairment, mobility impairment, intellectual impairment. Those non exhaustive impairments are compatible with the World Health Organization classification."@en ;
                   rdfs:label "Impairment"@en .