Want to install Incisive add on to Cadence DFII using Installscape on Centos 6.

Do I tell Installscape where DFII installation is already and then install Incisive ?

Does Incisive have to be installed before Cadence DFII or can it be installed after the Cadence installation ?

Any special considerations for Centos ? Will Incisive work on Centos ?

Thank you.