diff --git a/docs/design_docs/datanode_recovery_design_0513_2021.md b/docs/design_docs/datanode_recovery_design_0513_2021.md
index e537679e45..6e3f35a470 100644
--- a/docs/design_docs/datanode_recovery_design_0513_2021.md
+++ b/docs/design_docs/datanode_recovery_design_0513_2021.md
@@ -8,11 +8,11 @@ update: 6.21.2021, by [Goose](https://github.com/XuanYang-cn)
 
 DataNode processes insert data and persist them.
 
-DataNode is based on flowgraph; each flowgraph cares about only one vchannel. There are ddl messages, dml
+DataNode is based on flowgraph; each flowgraph cares about only one vchannel. There are data definition language (DDL) messages, data manipulation language (DML)
 messages, and timetick messages inside one vchannel, FIFO log stream.
 
-One vchannel only contains dml messages of one collection. A collection consists of many segments, hence
-a vchannel contains dml messages of many segments. **Most importantly, the dml messages of the same segment can appear anywhere in vchannel.**
+One vchannel only contains DML messages of one collection. A collection consists of many segments, hence
+a vchannel contains DML messages of many segments. **Most importantly, the DML messages of the same segment can appear anywhere in vchannel.**
 
 ## What is the real meaning of DataNode recovery?