Integrating object and relational technologies

A precondition for integrating object-oriented and relational technologies is an integration of their respective models. A general approach to unifying the models is outlined. The essential features of the resulting model are that abstract data types (ADTs) provide the sole mechanism for encapsulating data and operations, an inheritance ordering on ADTs reflects common abstract interfaces and supports static typechecking, and there is a distinction between value and object ADT instances. Primitive data types provided by the model include atomic data and data structures. Instances of primitive data types are always values. An ADT is implemented using a primitive data type to store its state. What is normally in object-oriented terminology called a class, is called an ADT in the model discussed. Object-oriented databases (OODBs) often make use of class extents, which provide a useful indexing technique for objects. In the model discussed, extents appear as instances of ADTs whose state includes a set of objects plus a set of sub-extents