A data model for engineering design objects

Design objects in CAD applications have versions and participate in the construction of other more complex design objects. The author describes data model aspects of an experimental database system for CAD applications called Pegasus. The model is based on previously published work on extensible and object-oriented database systems. The novel idea of Pegasus is the reconciliation of two subtyping (inheritance) mechanisms: the first, called refinement, is based on the usual semantics of schema copying; the second, called extension, is based on the inheritance semantics between prototypes and their extensions. The author uses these modeling elements to show how generic and version objects as well as component occurrences of (generic or version) components can be modeled