Object-Orientation FAQ

The COCOON project was intended to extend the concepts and the
architecture of relational database management systems (DBMSs) beyond
nested relational to object-oriented ones. Based upon the nested
relational DBMS kernel DASDBS, we have built a prototype implementation
of the COCOON model. Key characteristics of COCOON are: generic,
set-oriented query and update operators similar to relational algebra
and SQL updates, respectively; object-preserving semantics of query
operators, which allows for the definition of updatable views; a
separation of the two aspects of programming language "classes": type
vs. collection; predicative description of collections, similar to
"defined concepts" in KL-One--like knowledge representation
languages; automatic classification of objects and views (positioning
in the class hierarchy); physical clustering of subobjects via the use
of nested relations as the internal storage structures; support for the
optimization of both, the physical DB design and query transformation,
by corresponding optimizers.

Project goals are:

- to develop a general formal framework for investigations of all
  kinds of schema changes in object-oriented database systems
  (including schema design, schema modification, schema tailoring, and
  schema integration);
- to find implementation techniques for evolving database schemas,
  such that changes on the logical level propagate automatically to
  adaptations of the physical level (without the need to modify all
  instances, if possible).

In their current paper [see below], schema evolution is used as
example of a general framework for change in OODBs, supporting change
on three levels of database objects: data objects, schema objects, and
meta-schema objects.

Contact: Markus Tresch <tresch@informatik.uni-ulm.de>

REFERENCES:
        M. Tresch and M.H. Scholl. "Meta Object Management
        and its Application to Database Evolution."  In
        _Proceedings of the Eleventh International
        Conference on the Entity-Relationship Approach",
        Karlsruhe, Germany, Oct 1992.  Springer Verlag (to
        appear).

> Encore (Brown University)
email:bpe@browncs.brown.edu

Encore is an object-oriented database system targeted at large scale
software engineering applications which are involved in data modeling.
It was developed at Brown University in the late 1980s.  It is notable
for its special support for long-lived (ie. cooperative) transactions,
popular in design applications, and its support for class versioning.
Objects are never converted, rather, classes are versioned, and the
user can specify filters to make old-style instances appear as new
instances to new applications (and vice versa).

References/Additional Information:

 [] Mary F. Fernandez. OBSERVER: A storage system
    object-oriented applications. Technical Report CS-90-27,
    Brown University, Providence, RI, 1990.

 [] Mark F. Hornick and Stanley B. Zdonik. A shared, segmented
    memory system for an object-oriented database. ACM
    Transactions on Office Information Systems, 5(1):70--95,
    January 1987.

 [] Andrea H. Skarra and Stanley B. Zdonik. Type evolution in an
    object-oriented database. In Research Directions in
    Object-Oriented Programming, MIT Press Series in Computer
    Systems, pages 393--415. MIT Press, Cambridge, MA, 1987. An
    early version of this paper appears in the OOPSLA '86
    proceedings.

 [] Andrea H. Skarra and Stanley B. Zdonik. Concurrency control
    for cooperating transactions in an object-oriented database.
    In Won. Kim and Frederick H. Lochovsky, editors,
    Object-Oriented Concepts, Databases and Applications.
    Addison-Wesley, Reading, MA, 1989.

FTP: Complete source can be found in wilma.cs.brown.edu/pub/encore.tar.Z
See also APPENDIX E.