What is the MLSLABEL Oracle datatype?

I've开发者_开发百科 come across a strange datatype in oracle called MLSLABEL. It's not listed on datatype docs, and is only valid for 'trusted oracle' (whatever that is). The documentation I could find on it is this. What is MLSLABEL, and what does it do?

MLSLABEL is (was?) a datatype used by Trusted Oracle, the foreunner of Oracle's Advanced Security Option. The Admin docs say it was included in regular Oracle for compatibility. Find out more.

Trusted Oracle as a brand was replaced by ASO with Oracle 9i (I think). I don't think MLSLABEL is used in ASO (I can't find anything in the relevant docs). It is still supported in modern versions of the database. probably for backwards compatibility:

SQL> select * from v$version;

BANNER
-----------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
PL/SQL Release 11.1.0.6.0 - Production
CORE    11.1.0.6.0      Production
TNS for 32-bit Windows: Version 11.1.0.6.0 - Production
NLSRTL Version 11.1.0.6.0 - Production

SQL> create table mls (id number, lbl mlslabel);

Table created.

SQL> 

If I recall correctly, it is used for a finer grained permission scheme. Oracle out of the box allows users to be granted permissions on views, tables, procs, etc. But if you need to limit access to users based on the value of a column in a record, I think that you can use Labels for that. On the other hand, I am not certain when you go to virtual private databases (VPDs), but that might not be what you are asking.