Modeling design object relationships in PEGASUS

A description is given of the preliminary data model design of a database system for CAD applications named Pegasus. The model is based on previously published work on extensible and object-oriented database systems. Novel ideas of the model that are presented include the use of relationship objects as a modeling construct to represent relationships of any degree, and replication and the reconciliation of two subtyping 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. These modeling elements are used to show how parts and assemblies (with their versions, components, etc.) can be modeled in the world of mechanical assembly design