Schema virtualization in object-oriented databases

A description is given of the concept and implementation techniques of schema virtualization in object-oriented databases. The objective of schema virtualization is to provide users with multiple views of a database. First, the notions of virtual classes and virtual schemata, which are natural extension of views in relational databases, is introduced. Then, procedures to convert a schema into a virtual one, as well as rules schemata and their conversion should satisfy, are discussed. The key issue of the design of virtual classes and virtual schemata is `regarding procedures as objects´. Closure properties of classes and schemata are also discussed. Finally, several implementation techniques for realizing schema virtualization in Smalltalk-80 are presented