by Farquad » November 24th, 2011, 10:31 am
They're needed for tracing or animation. a=animation, t=tracing. I think the omcom contains the common aspects of a and t. I've been using Rhapsody for years and I've learnt that I do not really need to know more than that. The OXF is the important one to understand.
So, if you are building without a or t then they're not needed.