CAD databases have been used to store design data and to integrate design tools in IC/VLSI design systems. However, the requirements for a "good" CAD database are much more complex than those for a conventional database. Due to both the complexity of various design processes and the enormous amount of data involved in a practical CAD database, we believe that a two-level hierarchical database including a global database and a set of local databases is necessary. In this paper, we propose a framework for such CAD databases. We concentrate on the overall system architecture.