I used event sourcing for this. We were doing recording of live interactions and wanted to know the state at any given time. So the "current" state of any item

I used event sourcing for this. We were doing recording of live interactions and wanted to know the state at any given time. So the "current" state of any item was the result of all events happening until now applied in order, the state at any given time was just the same, with another time boundary. Don't fear the computation, we were doing all this in CouchDB with list functions and never had huge performance problems. Range queries are present in all databases. Constructing the events properly so that they apply conveniently to any kind of state is a different kind of story.