DDI means Domino Directory Integrator.It
is a domino web server application that allows you customize the domino
authentication process when HTTP users login. It can also be used to
integrate various datasources as user directories, to authenticate users
either through a custom designed domino database view or against ODBC data sources. And you can customize which group the user should go according
to which directory contains his/her authentication info...
For more information, please refer:http://www.ntko.com