There's a very good article on understanding/configuring auditing in oracle found here:
http://docs.oracle.com/cd/B28359_01/network.111/b28531/auditing.htm#autoId8
Using that you can configure oracle to audit the events you want, wether it be to a local file, database table, etc... As I had previously mentioned there are two ways I've used for doing it, either log to a local file using the "OS" AUDIT_TRAIL value and pickup the events using a universal forwarder on the machine or you can configure the "DB,EXTENDED" value for AUDIT_TRAIL which will cause it to log to the SYS.AUD$ table. Then you would need to write a script that will connect to the database as a user and dump out the contents of the SYS.AUD$ table and then implement this script as a scripted input running every X-mins. As also previously mentioned depending on the load on your database, etc.. one option may be better over the other for you.
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