[phkahler]

In solvespace such curves are represented by handles to the two intersecting surfaces and a series of points along the curve. This is an exact representation (you can compute as many additional points on the curve as needed) but it's not analytic by any means. Exact NURBS curves are used when possible too.

[wheelie_boy]

Exactly, I'm sure you're familiar with the kinds of difficulties and complications that creates. Rather than representing that curve analytically, you have to keep track of the procedural tree that generated it. Then things like offsetting that curve, checking that curve for intersections, etc. are more complicated.

And then you export. Rather than exporting the entire procedural tree (which would require shipping the entire kernel), you approximate the curves with NURBS trimming curves. When you import from another CAD tool you need to deal with edges that only intersect within a given tolerance, and sometimes that tolerance is awful (Catia, I'm looking at you). Operations on toleranced edges are a huge source of complications.

And so on and so on. It would all be so much easier if the NURBS math could be exact