Keep attribute values unique

[Jan-Piet Mens <jpm@Retail-SC.com>]

Hello,

Users in my OpenLDAP directory have an `alias' attribute, which
is used in addition to the `uid' value to deliver mail to, i.e.
I can have mail delivered to uid@host.com or alias@host.com.

The `uid' attribute is kept unique because it forms the DN for
the person. So far, I've kept the `alias' attribute unique by
storing it (with other data) in an RDBMS which has a UNIQE INDEX
on the column. This is the constraint for not having multiple
case-insensitive aliases. I "synchronize" the RDBMS to the 
LDAP directory with a bunch of Perl scripts.

Now to the question: how do other people solve the problem of
keeping an attribute value unique over multiple entries in the
directory ?

I'd be interested in solutions and any comments.

Thanks and regards,
	-JP