let's say you have a WP-Q2A integration. if you are developing a WP plugin then:
first require qa-base.php:
and if you need more inc files:
it will be using external codes, it is simple and flexible. but ofcourse users will need to config it's path, there is no scaping that.
if you are developing a Q2A plugin and want to use WP functions:
it should do the job, if you want to integrate two WP and Q2A plugins also include:
What are you developing any way?