On Mar 5, 2008, at 7:44 AM, Aki Niemi wrote: > > The entity-tag is an opaque token to the subscriber. The > subscriber MUST NOT attempt to infer any meaning from the value > beyond a simple reference, or assume a specific formatting. > The > relationship between the current entity-tag and any future or > past entity-tags is undefined.
But we DO infer something -- if the entity tag has changed, then the object has changed. So we infer that the object has changed when we see a different entity tag. But if the object changes (and we miss the notification), then changes back (returning to the same entity tag value) then we can no longer infer that the object changed, because we have the same entity tag. We don't know that the object ever changed, and would assume that it had just always been the way it is. Thus our inference would be incorrect. While this may not matter to the state of the object, it might matter to our understanding of how the object arrived at that state. On the other hand, if the entity tag were unique for each version of the object, we'd at least know that there had been some state change in the object (which could have been a missed notification, or might have been a null-operation that just updated the timestamp). I have a vague, queasy feeling that this might turn out to be important for some applications. But perhaps I'm looking at this in the wrong way. For objects where this kind of state awareness matters, perhaps one could just require that the object in question include a timestamp, or better yet a serial number. -- Dean _______________________________________________ Sip mailing list https://www.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip
