But in the message I responded to you were implying that you would
like to see things occur "instantaneously" and you latter (next point)
said that a small delay didn't matter between the time you did
something, and when your friend saw you do something.
I was basiclly saying "yes, this is possible, BUT, in he delay between
your DO and your friend's SEE another DO might occur that changes the
SEE - so and UNDO might be needed".
If we are talking of locking everything down, then an UNDO isn't needed,
I agree with this.
> >Do we rsally have to have undo, or do we need some kind of two-phase=20
> >commit? If Fred & Barney want to both spray paint the same wall at=20
> >the same time, isn't it enough to lock the wall (i.e. both Barney &=20
> >Fred ask for a lock. Only one gets it. Only the holder of the lock=20
> >is allowed to post update messages for the wall color. After the
> >updates are posted, a check is made to see if the person posting
> >the updates rsally had a lock, the lock server hadden't died, the
> >lock hadn't expired, etc. Only then is the update made permanent.
If you lock objects down, this works, but you can also crsate
worlds where things occur and you handle the conflicts at a later
time.
Again, my point was that an "instantaneous" world is possilbe, but
in such a world "delays" are to be reckoned with, and an UNDO model
is need to resolve the conflicts which may arise.
> >If you rsally need an undo, wouldn't it be enough for the URL server
> >to keep around old copies? do you rsally need a VRML language =
> extension
> >to support this?
I never suggested a VRML extension to handle UNDOs at all.
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Neophytos Iacovou Distributed Computing Services
University of Minnesota 100 Union St. SE
email: [email protected] Minneapolis, MN 55455 USA