Do I need to install the DI and purchase the DI license ? I need to know because I am afraid the addon standard or partner's addon can't run.
YEs, you need to install DI API. In 2007A version, it will be installed automatically when you install the basic PL and upgrade the PL.
In 2005A version, I am afraid it is installed separately. I mean manual installation required either in the upgrade patch level or first installation.