Computer-aided software engineering (CASE) systems require a database system that must let designers logically associate documentation and source code, make annotations to record explanations and assumptions, and manage different versions of the software. The author reports the development of a database, Neptune, which demonstrates that hypertext provides an appropriate data model for CASE systems. Hypertext is a medium-grained, entity-relationship-like data model that lets information be structured arbitrarily and keeps a complete version history of both information and structure. Neptune achieves application independence by using a layered system architecture; at the bottom is a transaction-based server, the Hypertext Abstract Machine, and layered above it are applications and the user interface. The use of Neptune in the Dynamic Design CASE environment is discussed. >