extends Relation and RelationChain abstract classes in childs

app/repositories/orient_db/learning_object/relation.rb

 module OrientDb
   module LearningObject
-    class Relation
+    class Relation < OrientDb::Relation
       include OrientDb::Methods::EdgeMethods
 
       def initialize(learning_object)

app/repositories/orient_db/learning_object/relations_chain.rb

 module OrientDb
   module LearningObject
-    class RelationsChain
+    class RelationsChain < OrientDb::RelationChain
 
       def relations
         [

app/repositories/orient_db/subject/relation.rb

 module OrientDb
   module Subject
-    class Relation
+    class Relation < OrientDb::Relation
       include OrientDb::Methods::EdgeMethods
 
       def initialize(subject)

app/repositories/orient_db/subject/relations_chain.rb

 module OrientDb
   module Subject
-    class RelationsChain
+    class RelationsChain < OrientDb::RelationChain
 
       def relations
         [