Structure for supporting geometric tolerances in product definition systems for CIM

The basic components of product definition data needed in CIM includes the following: a solid model to define the nominal geometry, a feature model to capture the semantics of the geometry, and variational attributes to specify tolerances and finish. This paper outlines such a part definition system with particular emphasis being on the design and implementation of a data structure for information needed to support geometric tolerance frames, zone and material modifiers, and datum reference frames. Associations among tolerances, geometric entities, features, feature attributes, and relationships are incorporated in this structure. The system is extendable to new tolerance classes without any changes to the code. The structure also permits incorporation of rules and validation procedures.