One way to do this is: - have a way of working out which users can see which objects - whenever an object changes, note that all observers need to see an upda

One way to do this is: - have a way of working out which users can see which objects - whenever an object changes, note that all observers need to see an update - either push that notification to the user, or record it ready for the next time they poll - when a user sees "object X has been updated", have them poll for it's latest state (which may be "deleted"). Possible optimisation: you can decorate some or all the "X has changed" messages with the details of the change, creating a journal This assumes the server can act as a serialisation point for all updates and so provide a single coherent time-series. It also requires that the server be able to fail updates which are the result of stale UI data. (e.g. someone tries to edit an object someone else has deleted).