Comment #1 on issue 3322 by jannik.laval: [Kernel Dependencies] ClassDescription>>#updateInstanceFrom: http://code.google.com/p/pharo/issues/detail?id=3322 mail from Mariano: The problem is the class changes. If there are objects that or disk with an image semgment, you want to load back the segment, update their instances (of the class that changed), and then put them again on disk. To do this, ImageSegment puts its code in updateInstancesFrom: oldClass I don't know about announcements or SystemNotifier. If someone is already notifying a class change, then ImageSegment could be just registered there, be notified and wala, no dependency. But I am not sure if someone is notifying or how to do it (to add it).