I wrote a PL/SQL code for showing all NLS parameters executed throught Oracle iAS. The value of some parameters in NLS_SESSION_PARAMETER are different from using SQL query data by SQL*Plus (from client that not set any NLS parameters on) such as NLS_DATE_FORMAT = 'DD MON RRRR' from the PL/SQL code, NLS_DATE_FORMATE = 'DD-MON-RR' from SQL*Plus.

I would like to know where the value of each parameter in NLS_SESSION_PARAMETER table come from is and how I can force it to my format (from the server, not in the code -- DBMS.SET_NLS)?