DBA Auditing

 I want to know as a dba what other database users are doing in the database. Suppose I have  database users XXY and XXB.  They have privileges of creating any objects in APPS schema.  As a dba how I can know that what are the objects XXY and XXB have created in APPS schema.   These users don't have APPS schema password but they may need to create some objects in APPS schema.  To create any object in APPS schema they need to do following:

connect xxy/xxy

create table apps.aaa    Or

create trigger test_trigger apps.bbb

table aaa or trigger test_trigger is created in apps by xxy.  Now I want to know as a dba what are the DDL or DML commands (create table or create trigger) has been issued by the user XXY or XXB from their respective user logins.