- From: Lisa Dusseault <lisa@xythos.com>
- Date: Tue, 25 Feb 2003 17:07:10 -0800
- To: "'Clemm, Geoff'" <gclemm@rational.com>, "'Webdav WG'" <w3c-dist-auth@w3c.org>
Geoff said: "Just one comment on the statement "we've already discovered since 2518 was published that locks aren't the only tool required to prevent lost updates". I disagree ... locks are sufficient to prevent lost updates. If a client decides not to use the locking protocol correctly (i.e. by updating a resource for which it does not have a valid lock), then of course something additional is required, but for a client that uses the locking protocol properly, locks are the only tool required to prevent lost updates." This was back in November but I have so far failed to respond. Locks never did solve the "lost update" problem, precisely. (Etags alone are sufficient to prevent a user from overwriting another users changes.) Locks solve the "aggravated user" problem, which is when I've been working for six hours on a document, and when I try to save it to the server the server tells me somebody else made changes and do I want to overwrite those changes... So I lock the file to prevent other people from making changes while I work. I get to reserve the file until I submit all my changes. I'm never presented with a dialog saying "do you want to overwrite"... Ideally, that is. In reality, locks can be lost. The most common situation is probably when the client goes offline accidentally during an editing session. Users and client applications have no control over wireless, routers, power -- failures that can prevent the client from renewing a lock. So let's say you've lost your lock. The user has been editing while the lock existed, and they already made changes. When the client manages to reconnect to try to save, the lock is gone. Well, there are two situations: (1) The file changed while it was unlocked. That sucks, there's no choice but to prompt the user to find out what they want to do. (2) The file did *not* change while it was unlocked. Cool. Without bothering the user with difficult and annoying questions, the client can simply relock the file and save changes. Since (2) is much more common than one, and much more pleasant, the client would like to know when (2) is the case. Etags would solve this. That's why I claimed that locks alone did not entirely solve the lost-update problem. Lisa
Received on Tuesday, 25 February 2003 20:07:12 UTC