Add Subset categorization in README

README.md

@@ -130,6 +130,17 @@ For more detail on data origin please look at:
 - [Legislative Yuan Meetings and Gazettes](https://ppg.ly.gov.tw/ppg/)
 - [Legislative Yuan IVOD system](https://ivod.ly.gov.tw/)
 
+## Subset Categorization
+
+The naming of subset is after the rule `{term}-{session}` which means:
+
+- Term: Fixed period during which the elected legislators serve. The duration is 4 year for each term.
+- Session: From [Knowledge Base](https://www.ly.gov.tw/EngPages/Detail.aspx?nodeid=333&pid=43230) of Taiwan Legislative Yuan, session means:
+> Each year the Legislative Yuan shall hold two sessions of its own accord during the following Constitution regulated periods:
+> from February to the end of May, and from September to the end of December
+
+For each term 8 sessions is expected. `10-1`, `10-2`, ... , `10-8`
+
 ## Data Fields
 
 | Field name             | Description                                                                                             |
@@ -154,4 +165,4 @@ If you have any issue on the dataset. Please leave a discussion on it or contact
 
 報導者(The Reporter) data@twreporter.org 
 
-歐噴有限公司(OpenFun Ltd.) contact@openfun.tw
+歐噴有限公司(OpenFun Ltd.) contact@openfun.tw