diff --git a/refs/types.proto b/refs/types.proto
index e607f34..15355ae 100644
--- a/refs/types.proto
+++ b/refs/types.proto
@@ -9,7 +9,10 @@ option (gogoproto.stable_marshaler_all) = true;
 option (gogoproto.stringer_all) =  false;
 option (gogoproto.goproto_stringer_all) = false;
 
+// Address of object (container id + object id)
 message Address {
-    bytes ObjectID = 1[(gogoproto.customtype) = "ObjectID", (gogoproto.nullable) = false]; // UUID
-    bytes CID      = 2[(gogoproto.customtype) = "CID",      (gogoproto.nullable) = false]; // sha256
+    // ObjectID is an object identifier
+    bytes ObjectID = 1[(gogoproto.customtype) = "ObjectID", (gogoproto.nullable) = false];
+    // CID is container identifier
+    bytes CID      = 2[(gogoproto.customtype) = "CID",      (gogoproto.nullable) = false];
 }