data migration, view partials

DEV/README.md

@@ -175,6 +175,22 @@ It's **forbidden** to overwrite lang keys from Redmine or Easy Project.
 
 All text **must use** I18n and must be translated at least to EN.
 
+##### Active record migration
+
+In Easy project we recognize 2 types of migrations, data and schema. 
+
+Schema migrations handle only changes to schema of database.
+
+Data migrations which are always in **db/data** folder handle only changes of data.
+
+Only exception if removal of db entities, eg. columns which could implemented in either type.
+
+##### Overwriting of template / partial
+
+One plugin can completely replace template / partial of plugin which loaded sooner. This pattern could be used
+to implement changes, but only if you are rewriting more than 50 % of contents. In case of small addition create or use
+ [hook](http://www.redmine.org/projects/redmine/wiki/Hooks). Hook must be created in appropriate repository, generally in core.
+
 ##### Syntax checking
 
 Syntax error is not tolerated. MR with syntax errors in one of the supported version of language is returned.