How to clear relationship on new Revision?

There is no onRevision event that I'm aware of. By onVersion, I am assuming that you mean onBeforeVersion or onAfterVersion. If so, are you hooking the before or after event? I think you'll want to hook the after. Be aware that the Version events are fired whenever a new generation is created. Therefore, if you have an item A with item B relations, item A is generation 1 in the preliminary state, and you lock item A to make a change creating generation 2, then the version events will fire when you save item A. It's unlikely that this is the functionality you desire. If you are using the out of the box change processes, then one option is to make a modification to the PE_ChangeItemTransition method to delete the relationships from the new revisions when that method makes the new revisions of the affected items. Dennis