ABSTRACT
This chapter reviews the elements that are incorporated in Parts 041, 042 and 043, the standard for the exchange of product model data (STEP) application integrated resources (AIRs). The STEP proposals for architecture engineering and construction based models rely heavily on these AIRs. Part 041 deals with many of the contextual issues pertaining to part models. Part 043 deals with the origin, version and status of models, especially when embedded in other models. Part 043 is used by and references other Integrated Resources. The geometric entities in Part 042 include point, vector, curve and surface, for zero-, one-, and two-dimensional entities, respectively. The corresponding topological entities include vertex, edge, loop and face. The topology schema provides structures for composing geometric entities into more complex shapes. The Part 042 representation of the b-spline curve is a sequence of control points, the degree, flags denoting whether the curve is closed or self-intersecting.
