A computer-aided design apparatus generates a tree structure of coordinate systems defining the topology of a three-dimensional object to be fabricated. Coordinate systems are positioned and orientated in accordance with mathematical functions. The mathematical function positioning child coordinate systems has the identity of the parent coordinate systems as a variable, and the positions of the child coordinate systems vary relative to their parent coordinate systems according to the identity of the parent coordinate systems. Data defining the coordinate systems and connections is stored in a graph. Bases having a defined relationship are identified and three-dimensional content objects are added. Content objects are added using the same mathematical function, generating three-dimensional content objects in each of a plurality of coordinate systems. The function for generating the content objects has the identity of the coordinate systems as a variable, generating the content object in each coordinate system with a different shape.