diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/api/rest/AccessPath.java b/src/main/java/org/gcube/informationsystem/resourceregistry/api/rest/AccessPath.java
index bc2eab1..212c21b 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/api/rest/AccessPath.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/api/rest/AccessPath.java
@@ -29,4 +29,7 @@ public class AccessPath {
 	
 	public static final String POLYMORPHIC_PARAM = "polymorphic";
 	
+	public static final String REFERENCE = "reference";
+	public static final String DIRECTION = "direction";
+	
 }