1) In oracle, we have user_triggers, user_tables etc. for various objects. For constraints we have user_cons_priv and user_constraints. Similarly dba_% & all_%. For default values for columns in tables also, storage in DD exists.
2) Please give me a detailed list of what all is possible to be queried and seen similarly in DB2.
3) If some of them are not possible from DD, please give alternative methods apart from using control center.