Re: Versioning

[kempf%hplabsz@hplabs.HP.COM]

> I'd like to find out more about Zdonik's VERSIONED-OBJECT class.  Is
> this written up anywhere, or is source code available, or anything like
> that?  Thanks.

The paper in which Stan described VERSIONED-OBJECT came from some of
his earlier work (1985) and was from a symposium for which no proceedings
were published. Stan has refined this somewhat, and the following two
references describe the refinement:

"Maintaining Consistency in a Database with Changing Types", Stanley B.
Zdonik, SIGPLAN Notices, V21, #10, October, 1986, pp. 120-127.

"The Management of changing Types in an Object-Oriented Database,"
Andrea H. Skarra and Stanley B. Zdonik, OOPSLA 86 Proceedings, pp. 483-491.

Essentially, the refinement consists of viewing a versioned object as
a version set, with additions only on one end. A versioned set interface
is also defined for types (or classes, in CLOS terminology). A CLOS
metaclass could be used to implement the versioned sets, with the MOP
providing a level of abstraction which makes versioned objects look like
regular ones.

As far as source code goes, last I heard (in June), Stan was distributing his 
persistent object system, but I think it is pretty specific to Suns
since I think he implemented a device driver to improve database access
performance. It's also written in C and comes as part of the Garden 
programming environment. His net address is sbz%brown@csnet-relay.

		jak