I wanted to add that I have a niche justification for having UUID available in tool interface. My tool needed to scan user's current history in order to determine if user already had generated relevant datasets. If they didn't exist, my tool triggered the generation of them, and loaded them into user's current history. In other words, a caching system. Without the UUID, I'd theoretically have to scan a User's entire list of histories, looking for the cacheable data, and that is error prone too. (A history dataset caching mechanism also becomes a step towards workflows that have checkpoints, that can be restarted at a checkpoint). Damion