[pkj]

Thanks for the comprehensive clarification. Yes you are right that the use of revision-id would allow "first change to reach the server wins" for case (i). It would result in a simple and fair outcome. I did not see the mention of revision usage in the parent link. But it makes absolute sense.

Think we agree on case ii). On case iii) I still think that having 1 local and N-1 remote might be useful when we want to prioritize a particular writer over others. Borrowing the sales example from commenter jchrisa, consider a new user sales-head (local rule). He syncs the data uploaded by his sales folks (remote rule) and then goes offline. When he is done editing and comes online, he wants to make sure his delta takes precedence irrespective of any previous changes by sales folks during his being offline. Since he has local rule, his update will just win. Further, he does not want sales guys who were offline and come online after him to overwrite his last update immediately. I am assuming that the sales folks with "remote" rule will see the data with newer server version and accept it.

[smarx]

I suppose your scenario for (iii) is reasonable in the case of sharing a datastore among multiple users. In that case, you'd probably still want all of that user's devices to use the same conflict resolution strategy.

BTW, (for now) the Datastore API doesn't support sharing among multiple users.

Given the relationship the Datastore API has between the client and the server, it's also possible for a client to use a custom resolution rule (though this isn't yet exposed in any of our clients), which would let you do smarter things like look at the changes that were made and decide based on app-specific logic which one should win. I personally think that's a big advantage, but as I said, it's not one that's yet been fully realized.