《Data Models》.pdfVIP

Knowledge-Based Representation of Dimension Units in CAD Data Models Dieter Roller, Oliver Eck, Berthold Rieg, and Dirk Schäfer University of Stuttgart, Germany Key words: Representation of Dimension Units, Knowledge-Based Management Systems, Shared CAD Databases Abstract: This paper presents a knowledge-based approach to represent the dimension units of numerical values in CAD data models. Although numerical quantities are associated with dimension units in typical engineering data, these units are missing in most product data models. Some extended data models allow to store information about dimension units, but this information is limited to a fixed number of units and conversions between these units is limited to a small set of predefined calculations. The presented approach helps to model parts of the semantics of product data by extending numerical values to semantic entities that can be converted automatically. Further, the 2 evaluation of simple units (e.g. mm und cm) or more complex units (e.g. N=kg*m/s ) in arithmetical operations (e.g. addition, multiplication or division) is described. The approach works on any set of units with any complexity. Users are able to define new units by so-called reduce and substitute rules. In order to evaluate dimension units in arithmetical operations, all units are converted first into a standard form, using the defined reduce and substitute rules. Next, the dimension unit of the complete operation is calculated by reducing fractions, combining units, calculating numerical values, and converting the result of the complete