how I can get log from database in oracle?

Last day my head judge me because he face with some problem that he didnot has it before!

but I didnt do any thing with database and also our company CM database is so critical !

In this case can he proof what I do with database???

Oracle have any log!

some functaion updating in last 2days that I didnt update it开发者_如何学Python and he also...

please help me,how I can proof who do the mistake.

how I can find who with which user connect to database and update or change some thing...

You can see when database objects were last modified (recompiled/altered/created) this way:

SELECT object_name, last_ddl_time
FROM dba_objects
ORDER BY last_ddl_time DESC;

There are redo logs (which are used to recover from a backup), but they don't record the username, workstation or anything else that identifies who made a data change.