On Thu, Sep 10, 2015 at 06:19:20PM -0700, Randy Presuhn wrote:
> >> Let's look at a slightly more complex hypothetical case to tease
> >> out how folks *want* things to work. Assume the following have
> >> been defined:
> >>
> >> - base module M
> >> - augmentation Q
> >> - augmentation R
> >>
> >> On a server claiming to supporting the modules containing M, Q,
> >> and R, respectively, which of the following might one encounter
> >> concurrently?
> >>
> >> - plain M
> >> - M+Q
> >> - M+R
> >> - M+Q+R
> >
> >It depends on what you mean by "encounter" but in terms of datastore
> >validity the only possible answer IMO is M+Q+R.
>
> By "encounter" I mean if a client asks the server for all of its Ms,
> and the server also supports Q and R, are all of the Ms *guaranteed*
> to be M+Q+R, or is it possible that some of the Ms might lack Q or
> lack R of lack both? If what netmod gives us is strictly M+Q+R,
> how would one model a system inhabited by a mixture of the four
> kinds of Ms?
Retrieval is easy since a client is going to ignore data it does not
understand and the server is expected to report what makes sense from
the server's perspective. The question is relevant for writing: Is a
client programmed based on M going to work even if a server supports
M+Q, M+R, or M+Q+R? I believe the rule stated in section 7.15 of RFC
6020 wanted to achieve this by forbidding mandatory nodes in
augmentations.
Y26-02 says that a presence container may be used to avoid breaking an
old client. Frankly, it seems not totally clear to me what the
sentence in section 7.15 of RFC 6020 really means:
If the target node is in another module, then nodes added by the
augmentation MUST NOT be mandatory nodes (see Section 3.1).
Does this rule only apply to nodes directly added under the target
node or does it apply to the whole hierarchy added? In the later case,
this would still cause a problem with the presence container work
around.
The recent suggestion to replace MUST NOT with SHOULD NOT in this
sentence may be seen as a softer variant of Y26-01. However, I think
we would, in addition, have to describe when it is OK to have
mandatory nodes in augmentations and when not. Simply saying SHOULD
NOT instead of MUST NOT will not help people to understand the issues
around this.
When this issue was discussed in the past, it turned out to be
difficult to find someone to write the necessary text explaining when
augmenting mandatory nodes is safe and when not. Are we doing better
now?
/js
--
Juergen Schoenwaelder Jacobs University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
Fax: +49 421 200 3103 <http://www.jacobs-university.de/>
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