Update strategy transformation Use

Update strategy transformation can be used in two levels.

1)Mapping level
2)Session level

Mapping level:-Within a mapping you can use update strategy transf to flag rows for 

Insert
Update
Delete
Reject
 
Session level:-In session properties you have an option as
Treat source rows as-Data driven(by default)
Or you can choose insert,update,delete

For target tables you can set the following update strategy options.

Insert
Delete
Update
-Update as update
-update as insert
-update else insert.
Truncate table.