I just ran across this post from EWeek, Oracle Locks DBAs in the Vault.
A quick read of it shows that it's a security add on to restrict DBA
access to privacy data. A solution for audit requirements for thingslike Sarb-Ox and HIPAA.
A look at the Oracle Database Vault page on OTN, adds some more context:
What is Oracle Database Vault?You can read the rest of this blog entry at Oracle Data Vault.