Implementing "beans with history" as this page suggests will have extra
benefits for rich-client applications.  If a bean can compute its own
dirty state, the UI in the client can use this to enable/disable
features like the "save" command and can prompt to save before closing a
window containing dirty state.  A client app can also provide feedback
when a user has performed "undo" enough to reset the window to its
original state or manually resets the original values.