Steps toward a relational 3D system

Parametric 3D CAD systems are mainly history based. Problems arise, when a point or value depending on other items and not given as parameter, has to be changed to a given position or value. Some concepts of a 2D relational system can be transferred. In 2D a line can be tangent to 2 circles, in 3D a truncated cone can be tangent to 2 spheres. But in 3D systems many more classes are needed, because the system has to hold the relationships, the CSG-model and the B-rep representation. It is essential to hold the transformations distinct from the solids. So, when doing an animation with items built by Boolean operations, these operations do not have to be recomputed if the items change only their position and not their shape. When traversing the model propagating new values in the right order can be achieved by classes, derived from the already needed classes for writing the model-data to a stream. Feature modeling can be done by segment definitions and instances of the segments. These concepts are derived from the procedure concept in programming languages.