diff --git a/et_def/et_def.proto b/et_def/et_def.proto
index 965cec8..7bfb058 100644
--- a/et_def/et_def.proto
+++ b/et_def/et_def.proto
@@ -145,6 +145,7 @@ message Node {
   IOInfo inputs = 8;
   IOInfo outputs = 9;
   repeated AttributeProto attr = 10;
+  repeated uint64 parent = 11;
 }
 
 message IOInfo {