Michael Endres & Richard Schuster 
CAD*I Drafting Model [PDF ebook] 

The content of this book is an information model for technical drawings, the so-called "Drafting Model". The Drafting Model is a part of a complex information model describing product definition data, their applications and their representations. The definition of the information model is a central component of the development of STEP, a future international standard for the exchange of product defmition data. Here the Drafting Model particularly encloses descriptions for the representations of organizational drawing data, tolerances, dimensions and surface attributes such as surface fmish symbols (a survey of the whole content is shown in the figure above). Additional to that requirements for the Presentation Model concerning the representation of geometry as well as the integration process for both the Drafting and the Presentation Models are formulated. The extent of the Drafting Model is restricted to the application area "Mechanical Engineering". Within the Drafting Model the annotation representations are described on the one hand informally and on the other hand formally using a high level language for information modeling, EXPRESS. Principally the representations of the annotation are described according to the international drawing standards. Thus the semantics pertinent to the specific graphical appearance are maintained. The data structures provide formal descriptions of annotations at a high generation level, which means that a "way" is defmed how to generate these annotations.