An Object-Oriented Active Data Dictionary to Support Database Evolution

Abstract

The Multimedia database of SPRITE is the central repository in which all information concerning documents is stored, including the contents and logical structure. When SPRITE is used in some application environment, it must be possible to integrate new applications or customize the available ones. This is to be achieved by the extensibility function. Extensibility enables a database system to be modelled as an evolutionary object. The basic principles of achieving extensibility are modularity and reusability. It is generally recognized that the object- oriented approach can greatly help in achieving these extensibility goals (see chapter 11). In the same chapter, it is argued that implementation efficiency can be improved by adopting a hybrid organization, that is, a relation-based scheme is used on disk to speed up associative access and an object-based approach is used in main memory to facilitate manipulations of single objects. In the SPRITE database this is realized by means of an object- oriented layer around a commercially available relational system (Sybase — see chapter 7 for more details).