ave directory architecture, in which all changes have to be made at t
he master and replicated to slaves, results in a similarly architected system.
In a virtual meta-directory, multiple directories synchronize with one another, but there is no central repository. When a directory gets a query it cannot satisfy, it refers the query to another directory. This is possible, for instance, using the X.500 standard or LDAP 2 referrals. As Novell Directory Services (NDS) and StreetTalk are ported to more platforms, you can achieve a similar effect using these products, which implement multimaster replication, in which any replica can be changed and all others will be updated.
There is a third alternative: client-based integration. In it, a single client talks to multiple directories through a single interface. This requires no changes on the back end but doesn't provide the management advantages or the unified programming environment of a global directory. LDAP-based clients, by themselves, give you no more than this.
Physical and Virtual Meta-Directories
