diff --git a/api/s31_scada_element.py b/api/s31_scada_element.py
index 5b1f522..457def3 100644
--- a/api/s31_scada_element.py
+++ b/api/s31_scada_element.py
@@ -179,5 +179,19 @@ def get_all_scada_element_ids(name: str) -> list[str]:
         result.append(str(row['id']))
     return result
 
+#
+# create table scada_element
+# (
+#   id text primary key
+# , x float8 not null
+# , y float8 not null
+# , device_id text references scada_device(id)
+# , model_id varchar(32) -- add constraint in API
+# , model_type scada_model_type
+# , status scada_element_status not null default 'OFF'
+# );
+#
+# 返回list，list里每个item是dict，内容是 'id':'abc' 这样
+# scada_model type 是类似pressure，flow之类的，是由Device 决定 的
 def get_all_scada_elements(name: str) -> list[dict[str, Any]]:
     return read_all(name, 'select * from scada_element order by id')