- From: Yaron Goland <yarong@microsoft.com>
- Date: Sun, 22 Feb 1998 22:42:39 -0800
- To: "'Judith Slein'" <slein@wrc.xerox.com>, "'w3c-dist-auth@w3.org'" <w3c-dist-auth@w3.org>
Amen. Yaron > -----Original Message----- > From: Judith Slein [SMTP:slein@wrc.xerox.com] > Sent: Thursday, February 19, 1998 8:54 AM > To: 'w3c-dist-auth@w3.org' > Cc: Yaron Goland > Subject: RE: "Lost Updates" still persist > > If we decide to go the "Implementation Note" route, I would suggest > something more like the following for the new text. The idea is to state > clearly what the problem is, why the protocol can't solve it, and what > clients and servers can do to help the situation. > > 4.3 Usage Considerations > > Although the locking mechanisms specified here provide some help in > preventing lost updates, they cannot guarantee that updates will never be > lost. Consider the following scenario: > > Two clients A and B are interested in editing the file 'index.html'. > Client A is an HTTP client rather than a WebDAV client, and so does not > know how to do locking. > > Client A doesn't lock the document, but does a GET and begins > editing. > Client B does a LOCK, does a GET and begins editing. > Client B finishes editing, does a PUT, then an UNLOCK. > Client A does a PUT, overwriting and losing all of B's changes. > > There are several reasons why the WebDAV protocol itself cannot prevent > this situation. First, it cannot force all clients to use locking because > it must be compatible with HTTP clients that do not comprehend locking. > Second, it cannot require servers to support locking because of the > variety > of configuration management systems, some of which rely on reservations > and > merging rather than on locking. Finally, being stateless, it cannot > enforce a sequence of operations like LOCK / GET / PUT / UNLOCK. > > WebDAV servers that support locking can reduce the likelihood that clients > will accidentally overwrite each other's changes by requiring clients to > lock resources before accessing them. Such servers would effectively > exclude HTTP 1.0 and HTTP 1.1 clients. > > WebDAV clients can be good citizens by using a lock / retrieve / write / > unlock sequence of operations (at least by default) whenever they interact > with a WebDAV server that supports locking. > > HTTP 1.1 clients can be good citizens, avoiding overwriting other clients' > changes, by using entity tags in If-Match headers with any requests that > would modify resources. > > Information managers may attempt to prevent overwrites by implementing > client-side procedures requiring locking before accessing WebDAV > resources. > > --Judy > > > > > Name: Judith A. Slein > E-Mail: slein@wrc.xerox.com > Phone: (716) 422-5169 > Fax: (716) 422-2938 > > Xerox Corporation > Mail Stop 105-50C > 800 Phillips Road > Webster, NY 14580
Received on Monday, 23 February 1998 01:46:36 UTC