Doug,
Good answer, most of it was generic enough to apply
I have mentioned I-deas specifically in the above mess, because some
> of the terminology is specific to it. I-deas really is different from
> almost every other CAD system in a number of key ways; namely, hybrid
> modeling, variational math, shared multi-user global coordinates,
> integrated data management...
Yea, I-deas was(is) different. One of those differences is that, internally, it represents all geometry as NURBS formulations. This includes lines and arcs which are degree one, and degree two NURBS respectively. Not a big deal until you IGES a model into a CAM system and find that all your planar arcs don't have center points. Stll, only an annoyance.
So.. I guess "lines are lines" isn't allways true.
Regards
Mark