DIMENSIONING AND

In design and manufacturing, many systems are used to manage technical product data. Each system has its own data formats so the same information has to be entered multiple times into multiple systems, leading to redundancy and errors. Although not unique to manufac-turing, it is more acute there because design data are complex and three-dimensional (3D). The National Institute of Standards and Technology has estimated that data incompatibility is a $90 billion problem for the U.S. manufacturing industry.1 Over the years many solutions have been proposed. The most successful have been standards for data exchange. The first ones were national and focused on geometric data exchange. They include the Standard d’Exchange et de Transfer (SET) in France, the Verband des Automobilindustrie FlächenSchnittstelle (VDAFS) in Germany, and the Initial Graphics Exchange Specification (IGES) in the United States. Later a grand unifying effort was started by the International Organization for Standardization (ISO) to produce one international standard for all aspects of technical product data, named STEP for the Standard for Product Model Data.2 The types of systems that use STEP are shown in Fig. 1. Nearly every major CAD/CAM system now contains a module to read and write data defined by one of the STEP application protocols (APs). In the United States the most commonly implemented protocol is AP-203. This protocol is used to exchange data describ-ing designs represented as solid models and assemblies of solid models. In Europe a very similar protocol called AP-214 performs the same function