On Mon, Aug 24, 2015 at 2:24 PM, Robert Wilton <rwil...@cisco.com> wrote:
> Hi Randy,
>
> On 24/08/2015 20:20, Randy Presuhn wrote:
>
>> Hi -
>>
>> From: Ladislav Lhotka <lho...@nic.cz>
>>> Sent: Aug 24, 2015 11:44 AM
>>> To: Andy Bierman <a...@yumaworks.com>
>>> Cc: "netmod@ietf.org" <netmod@ietf.org>
>>> Subject: Re: [netmod] Y26 again, sorry
>>>
>> ...
>>
>>> YANG does not provide any mechanism to REQUIRE modules A and B
>>>> to both be implemented on a server. You may think it should, but
>>>> currently the YANG conformance is for an individual module.
>>>>
>>> There are sections on conformance and conformance announcement,
>>> and they say nothing like this. In my view, the data model comprises
>>> *all* modules advertised by the server. I think your interpretation
>>> of conformance might be an extrapolation from SNMP/SMI times, but,
>>> for better or worse, it really has no support in the YANG spec.
>>>
>> It sounds as though you might be talking past each other.
>> I believe part of Andy's point is that clients will need to deal
>> with servers that do not implement (and thus do not advertise)
>> the augmenting module. But there's (I think) a more interesting
>> issue beneath this.
>>
>> Let's start with module M. Let's say M is for "modem" (to pick
>> an obsolete but widely understood resource).
>> Two different augmenting modules, F (for FSK - frequency
>> shift keying) and Q (for QAM - quadrature amplitude modulation)
>> are developed. Let us say that F and Q are mutually incompatible.
>>
>> A system with multiple Ms could well have both M+F and M+Q modems,
>> but (if we claim F & Q are incompatible) could not have M+F+Q.
>> If naked M is to be prohibited in systems (also) supporting F or Q
>> or both, we don't currently have a mechanism to do so.
>>
> Could this be achieved by augmenting from a choice statement?
>
> M defines the choice statement but with no case statements.
>
> F and Q both implement separate case statements that augment the choice
> statement in M. The case statements have containers which hold the
> parameters related to F or Q.
>
> M without F or Q is meaningless.
> M+F or M+Q works, but the choice statement means that you cannot have
> M+F+Q.
>
>
nice solution
This is perhaps the cleanest way to add mandatory nodes to a module.
The old client will not attempt to create the new case.
As I said before, I am OK with changing MUST NOT to SHOULD NOT
add mandatory nodes, and then add MAY when X, Y, Z conditions are met.
Two conditions so far:
(1) augment + when <new flag set that old client will not set>
(2) augment choice with a new case-stmt
(1) is hard to define, but not (2)
I can point you to a concrete example if it helps.
>
> Thanks,
> Rob
>
>
>
>>
Andy
> Randy
>>
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