The ORION-2 model of a federated, distributed, object-oriented DBMS is implemented at the Microelectronics and Computer Technology Corporation. The context of the federated system in this paper is a homogeneous, rather than heterogeneous, distributed system. A model of the federated system is such that each user has a single system image consisting of the entire shared database and the user’s own private databases, if any. Operations discussed under this model are populating the databases, checkout, query, checkin, and migration. The database schema in this distributed system is managed by the single schema approach, in which private databases and shared databases form a single hierarchy. The problems of managing redundancies and potential inconsistencies among the private databases and shared databases are not discussed, however. Versions of objects are also managed by a single hierarchy, in which all users share a single logical version-derivation hierarchy.

The paper is clearly written and instructive, although it could have been much more readable with more concrete examples. In order to properly understand this paper, the reader should have an introductory understanding of both object-oriented databases, especially query processing and schema management (see Kim [1]), and distributed databases, which are covered in many standard database textbooks.