STEP-standard for the exchange of product model data

The ability to interchange the design intent captured by mechanical CAD systems has been a recognised business requirement since the mid seventies. STEP is the name given to the evolving standard for product model data designed under the aegis of ISO TC184 SC4. Key elements in the development of STEP are the existence of three levels, namely information modelling, conceptional modelling and the exchange format, analogues to the application, conceptual and physical layers of the ANSI SPARC Database Architecture. A full and common understanding of the information contained in the product data is essential to designing a representation capable of capturing that information. Languages such as IDEFIX and NIAM are used by application specialists, usually from engineering companies. This information is then represented in EXPRESS, a data definition language evolving as part of the STEP activity to ensure that the data does capture all of the information content. The STEP definition is thus in EXPRESS and is human-readable as well as machine-readable. EXPRESS is a data definition language and does not represent instances