From W3C Wiki
email vs. wiki is an interesting example of the sigma/delta duality. Sigma (sum) and Delta (change from that). See DeltaView.
oh... that reminds me.. I have a TAG action item to write about the duality between message passing and shared state -- DanConnolly
...and that reminds me, I wanted to write somewhere about a problem of rebuilding a representation of current state from an event log... namely knowing when it's safe to make closed world assumption, ie. knowing when you've got descriptions of all relevant events, to make some pragmatic ClosedWorldAssumptions. I think this might be the 'frame problem' in disguise...' --DanBri
cf Paper Trail design issues note, TimBL, Feb 1999
hmm... this seems to be a ProxyTopic...
Well, how much of the current state are you representing? If it's not all of it, you don't need completely ClosedWorldAssumptions, just enough to know that the events which have been missed wouldn't put the system in a different coset from where you think it may be. (how orthogonal are the events?)