diff --git a/doc/data_structures.md b/doc/data_structures.md
index 8626d98..d77a160 100644
--- a/doc/data_structures.md
+++ b/doc/data_structures.md
@@ -1,3 +1,5 @@
+## TODO update
+
 ## database.pkl
 
 - **iid** (int)ernal structure id (can change at any update)