Subject: RE: Extensbility and Versioning Paces

From: "David Orchard" <[email-masked]>
Date: Wed, 15 Sep 2004 07:43:55 -0700

I've heard the issue about scoping of mustUnderstand before.  I think I
had suggested earlier on the list [1] 

> -----Original Message-----
> From: [email-masked] [mailto:owner-atom-
> [email-masked]] On Behalf Of Mark Baker
> Sent: Tuesday, September 14, 2004 10:07 PM
> To: Atom-Syntax
> Subject: Re: Extensbility and Versioning Paces
> 
> 
> I'm -1 on PaceAltExtensibilityAndVersioning, and -0 on
> PaceExtensibilityAndVersioning.  I do believe that the latter is a far
> better starting point (i.e. minus explicit versioning), but I think
the
> use of mandatory extensions is too simplistic as it doesn't consider
> the scope of those extensions.
> 
> Consider that the pace currently says;
> 
> 'An atom compliant processor MUST process all elements marked with
> mustUnderstand="true" or process none at all.'
> 
> which says to me that if there's just one entry in a feed which has a
> mandatory extension that isn't understood, that the entire feed is
then
> not processable.  I don't believe that this behaviour is what is
> desired.  So I'd propose that mandatory extensions be scoped such that
> having them on a feed means the whole feed will be rejected when not
> understood, but having them on an entry just means that the entry will
> be.  This brings up the issue of how scopes can be extended, such as
if
> somebody wanted to extend Atom with a sibling to entry, but I think it
> would be overkill to go there yet.
> 
> I also believe that any proposal for an extensibility mechanism that
> introduces mandatory extensions needs to change the name of the media
> type, at least when there's deployed code which supports the old media
> type.  This is because that old code has no knowledge of the addition
> of mandatory extensions and therefore will not behave properly when
> confronted with them.
> 
> I'm working on PaceExtensibilityAndVersioning2, but it's getting late
> and I won't finish it tonight.  I should have some time tomorrow
night.
> 
> Mark.
> --
> Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca