CAD boundary structures
Boundary structures were introduced for representing volumes in CAD-systems by Ian Braid  in his Ph.D. thesis from 1974. This triggered an extensive research in the second half of the 1970es and the 1980es into data structures for CAD.
Soon many CAD-systems included boundary structures. However, although the implementation followed the same basic ideas, the implementations were different and exchange of volume models between CAD-systems was almost impossible. The answer to this was first introduction of national standards and de facto industrial standards (such as VDA-FS, SET and IGES). However, by the end of the 1980es the STEP (ISO 10303) standard was introduced and a common data structure for exchange of CAD volume models was introduced.
The boundary structure has two types of objects:
Data structures describes how:
 Braid, I.C., Designing with volumes, Ph.D. Thesis, Cambridge University, England, (1974).