> [1]  http://web.cecs.pdx.edu/~black/publications/ModelExtensions.pdf

On page 22 of this paper, you mentioned that the notification
mechanism should tell you the previous values of classes and
methods for the purpose of cache invalidation. 

Goran and I made just these changes to SystemChangeNotifier in
Squeak as part of our DeltaStreams project; now, when classes,
methods, and class comments are changed, a notification with both
the old and new version is sent. It is completely
backward-compatible with the old SystemChangeNotifier protocol,
as far as we can tell:

http://map.squeak.org/packagebyname/deltastreamfixes

In the future (a month or two), I'm going to augment the
notifier again to support grouping of related changes, such as
all changes involved in loading a package, filing-in a
changeset, or loading a bug-fix, so that the enhanced logging
features of DeltaStreams can show system changes at more the
level the user made them; loading a package was a single-action
to them; the log should show it as a single action.

-- 
Matthew Fulmer -- http://mtfulmer.wordpress.com/
Help improve Squeak Documentation: http://wiki.squeak.org/squeak/808