diff --git a/spec.ttl b/spec.ttl
index fe25d9b..aa92c32 100644
--- a/spec.ttl
+++ b/spec.ttl
@@ -34,6 +34,15 @@ spec:Specification
   rdfs:label "Specification"@en ;
   rdfs:isDefinedBy spec: .
 
+spec:ClassOfProduct
+  a rdfs:Class ;
+  rdfs:label "Class of Product"@en .
+
+spec:definesConformanceFor
+  a rdf:Property, owl:ObjectProperty ;
+  rdfs:label "defines conformance for"@en ;
+  rdfs:range spec:ClassOfProduct .
+
 spec:requirement
   a rdf:Property, owl:ObjectProperty ;
   rdfs:label "requirement"@en ;
@@ -51,7 +60,8 @@ spec:requirementLevel
 spec:requirementSubject
   a rdf:Property, owl:ObjectProperty ;
   rdfs:label "requirement subject"@en ;
-  rdfs:domain spec:Requirement .
+  rdfs:domain spec:Requirement ;
+  rdfs:range spec:ClassOfProduct .
 
 spec:requirementReference
   a rdf:Property, owl:ObjectProperty ;