This article is from the Object-Oriented Technology FAQ, by Bob Hathaway firstname.lastname@example.org with numerous contributions by others.
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).
 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,
 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
 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.