Generalized Version Control in an

An important function of an engineering database management system is to support incremental and cooperative design in an orderly way. This calls for a version control mechanism of some generality if it is to be appropriate to the design of complex objects. We begin by considering the nature of design objects, and develop ing some functional requirements for version control of such objects, before outlining the basic object-oriented database model which we take as the foundation for our proposal. We then discuss the relationship between versions and the objects they exemplify, describe the mechanisms for the creation of versioned objects and the conversion of non-versioned objects to versioned form, study the impact on referencing and type checking in the object model, and arrive at a flexible notion of a context containing rules for version selection. We also describe our implementation of some of these concepts.