Operational transformation and collaboration in real time

Question

After reading this post (probably, you can get the gist by looking at the images, no need to read the whole text), I'm having a hard time deciding at which point is needed the help of comet type technologies. It looks to me (naively) that all of that can be accomplished by using ajax requests and a database to retrieve several versions. Is that true?.

Probably I'm missing something, so a clarification would be great.

UPDATE: Given the helpful answer written by Andrew, saying that an ajax approach to this issue it is not timely, I was wondering why, that is, at which stage the response sent by the server to the client will produce a delay?.

Answer 1

Comet IS Ajax requests.

In order for the server to be able to push notifications to the users browsers(IE anytime you see the server sending a change in the diagrams), the user needs to have a connection with the server already. The method of maintaining that connection using ajax long polling or the like is what the term comet refers to.

Yes, you could implement this by sending an Ajax request every x seconds. But that is wasteful, and it is not timely.

[Edit]

When I say it's not timely, what I am saying is that, using an ajax call to update on an interval will have a delay of whatever that interval is. The server CANNOT send an update to the client. It can only answer requests from the client. So if the server gets new information, it has to sit on it until all the clients come back and ask for an update. In a scenario like this people can edit the same information and commit it at the same time, which needs to be handled by the server, and which is what the article is addressing. Using a comet framework will just reduce the chances of this happening because the different clients will be better synced.