A new data abstraction layer required for OODBMS

A `class´ in the object-oriented paradigm represents both interface and implementation of the class. However, interface and implementation of a class are needed for different purposes, since class interface is shared among most users, while class implementation is used only by the implementers of the class. The authors introduce a new level of data abstraction, called the `class-implementation level´, which is based on separate management of interface and implementation of a class. They also describe a new model for OODBMS which provides users with the abstract view of the class implementation