5:30 a.m.
On Jan 9, 2011, at 18:17 , Chris G wrote:
> Sync peers all have slightly differening ideas of the concept
"calendar item" or "contact", so the real challenge is not just to
find which side has most recent data, but especially which data is available at one side
at all. If you just choose "most recent", you'll eventually loose all data
but what the dumbest (most limited) sync participant can store.
>
> Just imagine a mobile which stores name and tel numbers, but no postal address. If
the most recent update (say, to a telephone number) comes from such a device, there's
a whole lot of field by field merging magic needed to avoid loosing the postal address a
more capable device might have.
I'm designing (in my mind) the way the data is stored as well as the
synchronisation system.
If the data is stored as one file per record - e.g. each address/contacts
entry is a separate file then I see no major issue. *Both* ends store
all the data, name, address, phone number, E-Mail and whatever. Then
an rsync type approach of always keeping the latest one will work pretty
well - the only case it won't handle is if both ends are changed between
synchronisation runs.
I see. However this is more a file based approach to database replication than to PDA
sync.
You postulate that all peers need to understand one common format for each data type. This
is something that I've never seen happen in reality. Not even plain text is always
exchangeable without conversions (line ends, character set), yet alone more complex
structured data.
So while it is certainly desirable to reduce the conversion needs as much as possible by
using data exchange formats that are as universally usable as possible, a sync
architecture IMHO always needs to deal with conversion.
By the way, no, I can't imagine a mobile which stores only names
and
telephone numbers! :-)
You're probably too young, then :-) These things have existed and I have some lying
around here.
Seriously, you're probably right regarding what we today consider PDA data, i.e.
contacts and calendar entries. We can more or less assume that modern back-ends for PDA
data are able to store everything for contacts and calendars (oops, Outlook IMHO still has
a fixed number of fields for telephone numbers...).
Part of the point of synchronising two devices
(for me anyway) is to have the same data on both, by which I mean *all*
of the same data for a given person.
And that *all* will continue to expand. Today it's tel+email+postal+im. But what's
with the most recent blog entry, geo coordinate, twitter status, hires photo, github
commit? And the relation between all this? Even simple meeting invitations is something
today's backend often have a hard time to get right.
All of this will eventually become (if it hasn't already) part of what we today call a
"contact". But capabilities will be added to some systems sooner than to others.
With the result that we'll have quite similar situations as my (admittedly a bit
outdated) device-with-no-postal-address scenario, just on the next level.
I see no chance for a sync solutions that relies on *the* format that can represent
everything.
Lukas
Lukas Zeller, plan44.ch
luz(a)plan44.ch - www.plan44.ch