This paper discusses an ongoing research project to design and implement an object-oriented data management system for a mechanical CAD environment. This system will manage hierarchically structured objects stored in main memory and secondary storage. Recent work has been devoted to a requirements analysis for the data model of this system. To aid in identifying these requirements, an object-oriented solid modeling system was developed. We give a brief overview of this system, discuss requirements for the data model, and present the first version of this data model.