The structure simplifies creation/reading surfaces & solids.
Each surface/solid consists of boundaries (chains of opened/closed elements) linked together by rules (sets of curves of some type).
There should be at least 2 boundaries (with, obviously, 1 set of rules between them).
MUshakov, 04032010
Corresponding C++ library: DG_Db
File: Dg3DObject.h
Module: API Reference