We describe a semantic object-oriented data model for representing how a complex design database evolves over time structural relationships, introduced by the data management system, are imposed on the objects created by existing CAD tools. the relationships supported by the model are (1) Version histories (2) time varying configurations and( 3) equivalences among objects of different types we describe mechanisms for (1) identifying current versions (2) supporting dynamic configuration binding and (3) verifying equivalence relationships the data model is being implemented in a version server, under development at the university of California, Berkeley.