Update Problem & HTTP

HTTP is a stateless protocol i.e. the HTTP server is not supposed to keep track of the state of each flow. Now, in this situation, how can we deal with  the "update problem" ?

http://www.w3.org/1999/04/Editing

The above is one way of dealing with it. This may also be called as "Optimistic Concurrency Control" i.e. check for conflicts before commit - dont take locks too early etc.

As i see it, the idea is basically that :

1. Using HEAD: Check if a document exists/was modified before issuing the PUT request, by using the HEAD request before actually issuing the PUT.
2. Using Entity Tag : On the server, reject the PUT if the etag of the file from the client being PUT, does not match the etag on the server.