[K12OSN] iCal

Tom Hoffman tom.hoffman at gmail.com
Wed May 3 22:25:24 UTC 2006

On 5/3/06, Ben Nickell <twinprism at athena.physics.isu.edu> wrote:
> Les Mikesell wrote:
> >On Wed, 2006-05-03 at 14:28, Ben Nickell wrote:
> >
> >
> >>I have set this up before on an Linux apache server with webdav enabled
> >>and ran into the following problems..
> >>
> >>Data corruption/data loss when access with multiple clients at the same
> >>time.  The calendars get corrupted.  (but this may be related to using
> >>beta mozilla calendar/sunbird clients on windows and Linux in addition
> >>to iCal on Mac.)
> >>
> >>
> >
> >Did you have multiple users that were allowed to write to the
> >same file?
> >
> >
> More the like same user from multiple systems.  For example, they  would
> have mozilla calendar on windows at home and Linux at work, iCal on a
> mac laptop.  They wouldn't shut down the home or work ones.   I think
> they had them configured to synchronize automatically, so often it would
> result in the file being accessed by 2 clients at once an corrupting the
> ical file.  Maybe this was because of bugs in Mozilla Calendar
> synchronization, because I didn't think webdav should allow that.

The problem is that there isn't a standard method of handling this
kind of iCalendar file publication.  iCal takes the simple/safe route
of assuming that only one client is going to publish and all the rest
will subscribe.  It makes no attempt to synchonize of do anything
sophisticated at all.  If you publish from  iCal, it overwrites
whatever is there.  If you publish from two different instances, it
simply isn't going to work.  It isn't designed to work that way.

OTOH, Mozilla Calendar is designed to do a naive sync.  Before
overwriting a calendar, it checks for changes and tries to not
overwrite them.  This is inherently unreliable for complex cases (not
to mention that Mozilla can't seem to finish a calendaring client in

Reliably syncing multiple calendars is actually a fairly difficult
problem.  Note that there is now a standard called CalDAV which lays
out how calendaring via WebDAV is supposed to work, but it isn't
really supported yet.

If I were you, I would try to impress upon them the limitations of
iCal's implementation.  It places the burden on the user not to screw
up their calendars.  The user is responsible for only posting changes
from one computer.  If they don't like that, they're going to need to
use some other system, and a web based system is going to be by far
the easiest to deal with.


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