understanding the trellis code

Hi,

Some time ago I discovered Trellis to solve some of my problems with
updating data in classes I use for simulations and numerical
experiments. Now I would like to understand the Trellis code somewhat
better, mostly out of curiosity and to improve my python skills. The
code, however, is not particularly revealing, at least not for me.
Does anybody have some tips where to begin? Otherwise, what algorithm
is used to check and setup  the dependencies between the attributes?
If I were to build this myself I think I would use some sort of
dependency graph. But I cannot find this anywhere in the code. What
ideas are used in Trellis to do this?

bye

Nicky