This paper focuses on the problem of management of CAD data by investigating the use of the software engineering principles of data abstraction and object-oriented programming as means for managing the volume and complexity of design data. It discusses how a data management system which manages abstract data types provides a framework for integrating a CAD environment by providing a single mechanism to manage data, programs, and the manipulation of the data with the programs. It also shows how two forms of abstraction, aggregation and generalization, can be used to model hierarchies of parts and components, and multiple design alternatives, respectively. These abstractions are then used to model the geometrical and topological data required to describe three-dimensional mechanical parts.