2. Geometric model extensions

The basic models in today's CAD/CAM systems are essentially geometric. However, a geometric model has a number of limitations, the two most important of which are that the information is incomplete (geometric only), and that the dimensions are nominal, which precludes any connection with manufacturing constraints. Hence the need to manage :

• on shape (geometry) ;

• technology ;

• tolerancing (macro- and micro-geometrics) ;

• on materials (physical or mechanical properties) ;

• specific to a given application (finite element calculations, CNC manufacturing, etc.);

• administrative (supplier referrals, etc.).

CAD system designers therefore quickly sought...