Most of user identities information are not stored in directory. They are stored in a database, a flat-file, or within legacy application. Virtual Directory is one of the newest invention which can help enterprise to expose and repurpose those identities. The process to make those identities available in a standard Directory Access Protocol (LDAP) is very straightforward. All you need to do is to use a mapping tool, commonly provided by Virtual Directory technology, to create a “pointer” from your existing user identities to your “virtual” Directory Information Tree.
You can check-out a flash demo here.