Time traveling applications

[Hans Meine]

On Tuesday 29 June 2010 11:40:16 John Tapsell wrote:
>   It seems that quite a few applications have the potential to show
> past information, and I'm thinking that it would be good to get a
> consistent GUI for this sorted out earlier rather than later.

Good idea!  While there'll probably not be a "one size fits all" solution, 
consistency may also be first approached via similarity.

>   Consider a file manager showing the contents of a folder at an
> earlier date.  Or Okular etc showing previous versions of a file using
> the same technology.  (Whether that is an SCM or filesystem
> snapshots).
> 
>   In my particular case, System Activity (ctrl+esc thing) could get
> process and system data for any previous time and date if "atop" is
> installed.  (atop logs that info every 10 mins).  But I wouldn't know
> how to expose this GUI wise.

Did you ever see "Time Machine" from OS X?  At first sight, it might be pure 
eye-candy, but what it does is quite useful actually (all from the top of my 
head):

1) It moves a finder window to the screen center, blends out the rest of the 
screen and substitutes a space background -> indication that you're "time 
traveling"

2) You get many "shadow" finder windows stacked behind each other -> 
indication which points in time are available

3) You can select the point in time by either clicking on the window in the 
stack, or by using a timeline at the right screen border -> easy interaction, 
i.e. choosing the point in time

Here's a review with some screenshots:
  http://arstechnica.com/apple/reviews/2007/10/mac-os-x-10-5.ars/14

In summary, what you need is
- a clear indication of *where in time you are*, and potentially
- a very clear sign that you're in the past (the available options will most 
certainly differ!)
- a clear indication of where you may go (in this context, time is probably 
not really continuous, but only certain snapshots are available)
- interaction (forward/backward incrementally, and/or jump to a position)

Since time is linear (does not fork, at least in most contexts), I think it is 
obvious that a visual depiction of the time axis makes sense.

Also, Sun^H^H^HOracle's ZFS snapshot integration in Gnome is relevant:
  http://blogs.sun.com/erwann/entry/zfs_on_the_desktop_zfs

Have a nice day,
  Hans