Object-Orientation FAQ

O2 (INRIA/O2 Technology)

This is an entry on schema evolution.  General papers on O2 are included.
We have implemented in O2 schema updates in our first release but
without NO IMPACT on the database (we have a design to implement
deferred update, but it is a paper design). However, users manage to
convert their instances by hand, using their O2 programs written
themselves, and with the aid of the following tools:
1- There is a set of predefined classes whose instances contain
   objects representing a schema (i.e., a Meta-schema). These classes
   may be used in a conversion program, they may even be extended by
   the programmer.
2- There is a save-restore program that allows to take an O2 database,
   save it on a file or a tape in a logical way (i.e., independent of
   the physical format of objects on disk), and restore it again on a
   (perhaps new release) of the system, in an empty database.
   Currently, when saving a database its schema is also saved. The
   next extension to this save/restore program will be to save the
   database without saving its schema, and then restore the database
   on a new version of that schema. The restore program will be able
   to perform automatically some conversions like "add attribute" or
   "delete attribute".
Schema updates with impact on the database will be implemented in future
releases.
[Fernando Velez <fernando@o2tech.fr>]
For more information on O2, consult the following REFERENCES:
        Francois Bancilhon, Claude Delobel, Paris
        Kanellakis.  "Building an Object-Oriented Database
        System: The Story of O2".  Morgan Kaufmann Series
        in Data Management Systems, San Mateo, Calif., 1992.
        F. Bancilhon, G. Barbette, V. Benzaken, C. Delobel,
        S. Gamerman, C. Lecluse, P. Pfeffer, P. Richard,
        and F. Velez.  "The Design and Implementation of
        O2, and Object-Oriented Database System".
        Advances in Object-Oriented Database Systems,
        Springer Verlag. (Lecture Notes in Computer Science
        series, Number 334.)
        C. Lecluse, P. Richard, and F. Velez. "O2, an
        Object-Oriented Data Model".  Proceedings of
        SIGMOD88.  Also appears in Zdonik and Maier,
        "Readings in Object-Oriented Database Systems",
        Morgan Kaufmann, 1990.
 ==== Corporate headquarters:
O2 Technology
7 Rue du Parc de clagny
78035 Versailles Cedex
France
tel : 33 1 30 84 77 77
fax : 33 1 30 84 77 90
[They have many other contacts worldwide]

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